What I think is that we very seldom know what is working our territory, unless you have camera's like I do. I don't see anything here, I just find the results or movies of them. A mink or weasel can go right through a 2X4 wire fence. I didn't have coyotes here until a year ago and they caused some serious damage and I had to change my mode of protection. After leaving a foot here they haven't come back...yet. Overall this place is pretty secure, but I don't beleive anything is totally secure. Electric fences are good. I have had two mink attacks here and they were devastating .... they kill everything in the pen. They are very curious though, so they are not that hard to catch. The two here were out during the day, so they went to mink heaven very quickly.
Walt
I second what Walt says. I suggest building your pens as tight and secure as you can because it is cheaper in the long run to do that then to have to re-do when some predator you didn't know you had comes looking or new one moves into your space. That happened to friends here, 20 years with birds and they never had a skunk. Then a skunk came in and dug under a pen and killed birds.
I use chain link fence on most of my pens, lined with chicken wire to keep out thieving wild birds, quail and doves are plentiful here. A few pens are 1" X 2" welded wire and I use that wire for tops on the chain link pens. I also keep turkeys and the chain link is good since they are big strong birds, they are not going to be bending wire.
Bobcats will do the same thing as minks, get in a pen and kill everything. I have not had a bobcat breach my pens the way they are set up now and there are lots of them around here.