Sadly, one of the first lessons you learn as a farmer, there's a lot of things that like nice easy dinners.
My neighbours have Livestock Guardian Dogs and haven't lost anything since they got them. Another friend has a llama with her sheep and with the right llama, she hasn't lost any, after her first llama died, she lost several to bears and cougars. A bear killed one of her replacement llamas. I don't know anyone who's had guardian donkeys so can't comment on how good they would be.
I have my property fenced with 4' field fence and a strand of electric 'hot' wire on the top, it keeps the bears out and slows the coyotes down. Had a huge bobcat kill a chicken a few weeks back, it climbed up the wooden post, hopped onto the roof of the chicken shed and then jumped down through the gill net covering the run, killed the rooster and then must have climbed a different post, they're only 5-6" diameter, and broke through the netting again and took off with it. I saw it in the morning and chased it off, but it came back later on. Chickens in those runs are locked in at the moment, another week and I'll have time to add another 4' of stucco wire to raise the fence up to 8'. You think you have it perfect and then another smarter or more determined animal comes along and proves there's still a way in.
Good luck with finding a solution.