Why don't you enclose the top? Basically a wire caged box. That way you can put platforms at different heights, with ramps and tunnels. Will give them different perspectives in order to view the world. If it's enclosed all the way around you won't have to worry about a Houdini cat.

This idea of an enclosure attracted me for awhile because of where I will be moving to in the next few years, I thought if I kept my cats outside in the backyard of a group home, then De clawing or allergies would never come up (outside year round with heated source in winter, never actually in the home with the people)

Better to have cats become half wild/or worse yet semi feral, then ones who have their front toes cut off and as a result possibly bite people and can no longer defend themselves from danger and/or get reliuqished to a shelter and PTS because some buddy gets Allergies. Mine are both neutered so even if that did happen (heaven forbid) no breeding.

However I think in the insane MN climate it wouldn't work in winter without expensive heating.

I want them to have more room than just a cage outside to run and play. There are apparently ways of angling in the top of the fence that the cat can't climb over - or make it out of plastic fencing that they can't climb. What I want to know is if this really does work as well as it sounds.

Heating it is not necessary. If they have free access to the outdoor pen, I expect the cats will go in and out continuously all day long - staying out only until they get cold and want to come in. That's what they do now (they have access to the porch & roof) but it gets really tiresome having to open and close the door for them every 5 minutes! That's why I'd like to just put in a pet door downstairs and let them do their own thing.

Yeah, yours don't live outdoor year round, which is ideal IMHO.

Basically unless you leash train them, or tie them up outside, your going to have issues with outdoor dangers unless you keep them strictly indoor. The question is, is it worth it to you. Outdoor cats are as a rule happier as they get to for fill all of their natural instincts but they don't live as long.

I have always leashed trained my cats. I use a harness with a long leash. They go out when I am out. Just beware, it does become a pain because they get in the habit of dashing outside when any door is open at any time. For this reason, you may want to reconsider them being allowed out.

A friend of mine did a fenced area like you are describing. It works but you have to be diligent about watching their actions for quite awhile so you can see where they have spotted possible escape routes. My friend noticed her cats eying the roof from the rail of the deck. They were contemplating jumping to the roof and then from there off the roof to freedom (and most likely the hiway). She solved that by putting a pipe in the rail so they couldn't get a good footing to jump with.

So anyhow she had chainlink for the main part. The top was made with long pieces of conduit bent to form a loose upside down "J". The conduit was wired to the fence posts and there was either wire mesh or netting over the bend. The bottom was secured with some heavy duty wire landscape staples so they couldn't push under it. I guess the concept is that they can't climb upside down and if you make the fence tall enough and the angled area large enough they can't jump on top of it. My friend also had one of her small basement windows replaced with a door of sorts that had a cat door in it so they could go in and out as they pleased. She has six cats and the whole time they lived at that house they never got out. There was a gate too but it was tricky and the top part had to be flipped up to use it and then put back. I might have a picture somewhere, I'll have to look.

I have a friend that purchased the purrfect fence. She had a small pet door installed in her spare bedroom window with steps down to the grass. She has had the fence for several years and only had a problem once. She had to string up a corner that was connected to the house, after a few years. I have heard her say that was the best thing she ever bought a million times. She often talks about buying another one and connecting the two with a tunnel.