Remember, though, that donkeys and such require care as well- so farrier, vet, feed bills- but are supposed to be good guard animals. There are also dog breeds that are bred specificlly for livestock protection, but as a general rule they need to be raised with the herd. They have their own associated costs, and aren't a quick fix. Guard donkeys (at least here) are often found that are free to whoever wants them and can haul them off.
If it's just these 2 dogs, I would set traps for them with bait. (live traps, not poison as it's illegal most areas and 2) not a good idea with other animals) Catch them and then do as you please. Around here, we get the small, occasional feral pack of domestic dogs that raise complete hell. Even though I love dogs, and I rescue, I won't hesitate to shoot any animal that is attacking mine on my property. My dog works well for chasing off nuisance animals (he's a 90lb catahoula) including dogs, coyotes, raccoons, hogs, etc.