Trees and deer, 2 worst enemies.
I usually check my fence charger, it tells me when I have a limb down. Cattle (at least mine) won't hardly cross a downed electric fence, they are so accustomed to avoiding it, even when I drop a wire, they wait for me to move it until they step over the old fence line.
My perimeter is electrified HT smooth wire with springs on some long runs. Limb falls and it just breaks plastic, run along with chainsaw and bag of retainers and it's usually pretty quick. Would hate to think what it would be like living where I live with barbed wire, I would do nothing but fix fence every afternoon here lately. Lots of storms and ridiculous amount of wind. Also, I keep different pastures on a switch so I don't have to check the entire line all the time, just the one they are in.
Ice storm years ago has had a long lasting effect, limbs and trees are dying at an even quicker rate than usual here lately. Lots of "widowmakers" hanging in those trees when you look up. A logger I talked to said he was just doing mercy killings. I like to keep our pasture pretty clean, and lately it's been a nightmare, at least in the woods I can just pile it to the side.