When it comes to predators the two that I've seen cause the most trouble are also the two that are the most persistent, foxes and Raccoons. The only good thing about a fox is that they will at least eat what they kill, coons seem to be butchers, killing every chook they can get their hands on and leaving them.
The methods I consider the best are 1). Electric wires, place on near ground level and one at the top of the run.
Even better two wires about 6" apart at the bottom and the same at the top.
2). Double fencing, 12 gauge 2 x 4 wire and heavy gauge 1/2" hardware cloth
Even better would be 1/2" rabbit cage wire but that is costly.
3). I have also used Wolf Urine but it takes a lot of it since you need it all the
way around the run and have to reapply after a rain. Put it on the posts, that is where a wolf
would mark territory.
4). Dogs work very well, ours have convinced most of the coons not to come onto our land even
though they are in a fenced in yard. I take the male out every few days for a walk,
he marks the run since it is his territory and this seems to be more effective than wolf urine.
5). Traps are ok but you then have to relocate the critter far from your place, coons can carry
some diseases and that can be troublesome if you should get bitten.
If the measures I've listed don't work then it is time to dispatch the critter, I use a scoped Ruger 10-22. This method is final and by the way, raccoon BBQ is very good tasting.
When we bought Buzzard's Roost we had a fox that came around every day, once our dogs marked over his markings, he has not been back.