The best thing that I have found (and I haven't found it again) is Creosote soaked rope. I have a whole roll of it, but the people I bought it from don't have anymore and can't remember where they got it. You cut of a good length and wrap it around the tree at pig shoulder height. They Love Creosote. Most guys use railroad ties for that reason, but carrying a railroad tie into the deepest parts isn't very practical. You just cut a length of this rope and make a rubbing pole anywhere. Great stuff. I have seen the exact thing dog1 has seen though. The big one I shot last week had cut pine trees ooozing pine tar all over where I shot him. You can usually tell you got a big one when those cuts and pine bark ripped off are waist high on you.