A mild soap water also works as a surfactant.

The most efficient commercial deterrents all contain putrefied eggs. Garlic and peppers will work to some extent. Scientists say the rotten egg smell mimics a well fed wolf's urine. How they know I couldn't tell you. You can use fresh eggs, pepper, garlic whatever with some vegetable oil to make it stick. Some people leave the egg mixture until it rots. Whew!

Bought Shake Away at a home center store. It's grainy and contains fox urine, safe for pets, it worked for me in the spring, darn furry critters.

I have been using Liquid Fence, but it washes off with the rains or sprinklers, as does the cayenne pepper that I have tried.... So I read about Bobbex --- Aha! It seems to be working better, does not have to be sprayed on as often, doesn't wash off as quickly. So - that's my suggestion. I've been very very very frustrated with the rabbits in my yard, so I feel your pain.

Be prepared - this stuff smells worse than anything you can imagine - but after it dries, the smell is only detected by the animals. Wear gloves and stand down-wind when you spray it (not on a really windy day!).

The good news that I can report is that as my plants get bigger, they seem less bothered by the rabbits - i.e. - they've been nipping off all the scapes on the younger plants, but the larger Rainforest Sunrise have bloomed without interference. Although these plants were chewed on quite a bit in early spring as they were just coming up (before I started using these products). Its a struggle. I keep hoping the foxes will return to the area!

I found some Liquid Fence Deer and Rabbit Repellent at Lowes. No rabbits here but deer were eating the tops of my tomato plants. It's only been three weeks, so I know it's not the best testimonial yet, but so far no more munching in my vegetable garden.

It's made with things like eggs, garlic, thyme oil, so not only cruelty free, but not as much worry if you get it on your skin or breathe it in, etc. Although it does stink at first before it dries. They say the deer and rabbits can smell it for a much longer time. But we get no rain so I don't have to refresh it that often.

I'm crossing my fingers it keeps on working.

The second time the Hostas were attacked was by deer (which weren't as picky between the two varieties). I bought and used Deer B Gon. It seems to have worked, but I can't be sure. At best it keeps them from eating the treated plant. Yesterday, they ate lily of the valley berries (which should be poisonous) right next to the treated remains of violets that they had eater earlier. Even on clearance sale Deer B Gon was a bit pricey for the number of plants I'll want to protect next summer. A nearby Asian foods store usually has much better than this linked price on this:

http://www.mysnacks.us/spices/spices-herbs-powder/swad-chilli-powder-extra-hot-14-oz-400-grams/ 

That is a delicious spice I use in cooking (about 8 oz per year). Tiny amounts make food too hot for most Americans, but the way I like. I expect that is lower cost per heat than other peppers. Is that likely to discourage deer and rabbits?