Hmm well walloping with poor timing might just get her kicked harder, donkeys don't take a lot of crap. That isn't to say that he should be allowed to do whatever he wants, on the contrary he shouldn't be allowed to get close enough to bite or kick unless he is invited into that space in a polite manner.

"It's really quite amazing what a horse will do for you, if he only understands what you want. 
And it it's also quite amazing what a horse will do to you if he doesn't." ~ Bill Dorrance