I don't know if this is feasible for you, depends on how many member you have, but at our CG, we only have about a dozen members. We have a padlock on the gate, and every year the members get a key (one of our members works at a hardware store and gets the keys copied for free). We also have very good neighbors beside the garden that watch our for "funny business".

There aren't many members but it is in a big open space next to an industrial building. They are providing the water. No fences, no neighbors. I don't know if it would do anything to post a sign saying I will prosecute. I am hoping folks will be out there a lot to make it look busy and maybe deter him that way.

You might have to stake out the garden and videotape him in action, then videotape him at the farmer's market with the goods.

If he's after the high-value produce, some of that has markings that are variable enough to make identifying a certain eggplant or tomato possible.

Then call the cops and make a theft complaint. With high-value veggies, it might even reach felony level.

Good luck. There are only a few members in our CG, it's surrounded by a tall fence and the gates are locked. Came back from vacation this spring to find someone had whacked the heads off every single sunflower!! It had to be one of us. You have to be a member of the neighborhood association to get a plot in the garden, most of us have been there for years. We've had eggplant and other things go missing. Sorry but noone is climbing a 10' chain link fence to steal a couple of eggplants! There aren't any needy people gardening with us that need to steal, the average income of my plot neighbors is over $100,000 per year, as a nurse I'm the poorest one in the garden.
Good luck.
Tally HO!

Put up a video surveillance sign :P Even if it is not true, might be of help.

This may not help everyone in the garden... But if you want to look out for #1....
-Plant the stuff that is hard to harvest near the entrance to your plot. Sugar snap peas, beans, carrots, beets (you get the idea.)
In the middle plant the good stuff ($$$$). Maybe srpinkle some stuff that looks like deadly ag chemicals near the entrance and close to the good stuff. Baby powder, dried out crushed egg shells. Maybe 'he' won't take it if won't command a price premium that organic veggies get.

We have fake surveillance cameras set up. Not sure if it works yet or not. Our community garden is at the church.

I do not think police will take veggie thefts seriously unless you live in a low crime area and they have plenty of time on their hands. Maybe picket near the farm market with his picture and "do not buy stolen produce" might cause a big blowup though!

I plan to put alarmed fake tomatoes in my plot. About $20 to make with store bought wireless window sensor alarms. Wish me luck.

It wont help with one person wanting to sell the crops of others but for those passing by that simply want a snack which I would guess is the biggest issue for most gardens a eat me garden may help. I am pushing for one in our garden this year. Eat me garden.... a spot/plot that belongs really to no one that has editables that will not be missed. A sign stating that If you must take something take it from here! or something to that effect. If anyone has one of these I'd love to know what was planted and if it has helped... I am new here so you can pm me if that is possible so we do not take over this post.

Ink tomatoes! Like the ones they have on clothing in stores!!!! Or ones that emit a terrible odor, like rotting garbage! As much as I hear about theft in community gardens, I'm really surprised no company has come up with something like this yet.

All kidding aside, a tall sturdy fence and a padlock might deter him. The fence could be really pretty with some non edible vines growing on them. A hedge of something thorny along the bottom might make cutting through the fence and crawling over not worth it. Maybe some really nasty roses; I hear New Dawn, a monster pink climbing rose has some gnarly thorns. That sucker grows +12ft. Then layer some raspberry brambles, and you've got a beautiful and bountiful fence San Quentin Pen would be jealous of.

It depends what neighborhood you're in. In some neighborhoods you could leave the doors to your house unlocked and be gone for a year and there would be nothing to worry about. In other neighborhoods, anything not bolted down will be gone within 24 hours. I was told about one incident where some thieves climbed over a high fence to steal someone's barbeque—a crappy cheap little one that the owner had actually picked up at a garage sale. Thieves have been known to actually dig out the bushes in people's front yards, in that particular neighborhood (which shall remain unnamed). It's really a shame that you can't even grow any vegetables without someone stealing them. Is this what the world has come to where we need a 24 hour armed guard to protect vegetables?

You ask how to prevent theft? Well, I'm not sure exactly how bad it is in your neighborhood, but you might locate your plot near an elderly person's house who spends all their time sitting on their porch, overlooking the garden. Then put up an electric fence with attack dogs to keep it safe at night.

Another idea might be motion-sensor activated cameras. They are used for hunting purposes and are surprisingly not too expensive. They can be camouflaged and easily hidden. So put the fake cameras near the entrance and hide these cameras in the garden. They can be set to only be activated at night (they have a light sensor).

Keep a shaker container handy (like the ones you see in the pizza shops) with plain old all purpose white flour. Sprinkle it regularly on your prized veggies when they are close to harvest time. It looks just like some of those nasty pesticide dusts. No one wants to eat that.

Or put up a prominent sign that reads: "We fertilize with organic human manure", with a picture of a big brown turd.

Or put up a sign with a skull and cross bones which that says something like "Experimental pesticide research, not for human consumption"

people probably stealing some vegerbles for erotic means. Eggplants make me uncomfortable and are forbidden at my church.

Eggplants are "forbidden" at your church? Are you joking?

That's the silliest thing I've ever heard. Do you stay away from carrots and zucchini too?

We put up a trail camera and told everyone about it. Got pictures of a couple people at night. Our Community Garden is run by the church so we cannot file charges against anyone. Its a no fence garden and most of our produce goes to the food bank and soup kitchen. They do not charge us for growing so it don't matter to most of us.

Maybe, if I didn't pull hundreds of pounds of discarded produce from the dumpsters during end of season garden cleanup, I'd be more upset about pilferage from our community gardens.

Most bountiful in garden dumpsters in my area: Peppers, tomatoes, tomatillos and potatoes.

Most often the whole plant is tossed with the veggies still attached. I also see hundreds of pounds of melons that were enjoyed by the wasps instead of the gardener. I have asked many many gardeners why they throw their produce out. Not as good as at the store is the answer every time.