Some ways a predators create/find a gap to get into an apparently predatorproof run:
- rip apart the wire (this includes chickenwire and cheap chainlink; and for a really motivated predator can include other kinds of wire as well)
- chew through the wire (mainly chickenwire, but also includes other kinds if you've attached them at seams with zipties or light-gauge wire)
- pry at an edge or seam of the wire til it bends enough to let the predator sneak through the gap
- rip the wire off the what it's attached to (raccoons, dogs and coyotes are FAR STRONGER at this than nearly everyone can possibly imagine)
- rip apart a piece of wood framing that the wire is attached to (that is, pull it off whatever it is nailed/screwed to, either by pulling out the fastener, or pulling the wood off over the fastener, or breaking the wood), especially likely once the fence has "aged" a bit
- push a fencepost over, (see comment about peoples' ability to imagine things), also likelier once fence has "aged"
- climb over the run (possums, raccoons, foxes, and some dogs are excellent climbers and can scale things you may think are unclimbable, like wood siding; some other predators will climb too) and do one of the abovementioned things to whatever top you may have on the run
- dig under (if you have dogs or foxes around, even burying the bottom edge of the fence 18" deep is not a guarantee of safety, nor is a 4' wide apron, and anything less than those is definitely for sure breachable by a number of predators)
- find an existing gap -- weasels can go through a 1" opening, young raccoons and possums can go through a 2x4" or 3x3" opening, a number of adult raccoons can go through a 4x4 or 3x6" opening, etc.
- push gate open enough (even if locked) to squeeze in the gap
- open or break or rip out the gate latch.
This is not an exhaustive list.
Really, spend a few hours in Predators and Pests to see how non-rare it is for people with really pretty stout runs to have predators get in.
If you are cool with risking it, that's fine, but it sure seems like a very large number of people just can't imagine it could ever happen to them, or figure that because Joe down the road has had chickens in a topless chickenwire pen for ten years there are obviously no predators around that could get into your own run. Which is not the way it works.
Just sayin',
Pat