I use cotton ripstop BDU's and love them. I used to wear dockers and also Levis, but with both of them when you get a little snag they will rip and not stop until your leg or ass is hanging out. The ripstop BDU take nicks (not from a chainsaw) very well, just looks like a little puff. They are tough pants, Propper is the brand name I think. Here in FL you need cool clothes, and these are much cooler and allow more range of motion than Levis. You can get them for about $30. at a army navy store.
Just 2 nights ago I was doing some rec. climbing in a liveoak in my front yard (night climbing is the best), and thought for sure I had just ripped them open, but they were fine. I was straddeling a large limb, rotated underneath it so I could then drop out of the tree, but I did it so quickly I could feel the bark biting me hard.
Greg