Donkeys eat meadow grasses and "weeds", but they also will eat tree leaves and even tree bark. They also love things like carrots and apples and, as you have learned, your ornamental lawn plants. There may be plants that donkeys won't eat but I don't know what they are and haven't been able to find a list for you. When the donkeys come back into your yard, you could watch to see what plants they avoid and then fill your yard with those plants; but I think what you are really going to need to do is to find a way to exclude the donkeys from your yard—or, at least, from the plants you don't want them to eat. You could consider fencing your yard to keep them out. Here are a couple of examples of fencing that would work to keep them out—one with 3 rails and one with 2 rails. These fences wouldn't spoil your view, but would certainly keep the donkeys out. You could also consider putting barriers around the plants you don't want them to eat. There are various kinds of fencing to keep out deer and other pests. You could enclose individual trees to protect the bark and place a barrier over and/or around flower beds. Good luck with the donkeys! I have four of my own and they are VERY smart—always figuring out ways to go where they shouldn't go and get into things they shouldn't get into.