Tell them that there are snakes up that tree, why would you want to climb there..........We have 1 very old crab apple tree, it is almost laying down, probably 50 to 70 years old. You can spray specricide on the missing bark and post a sign saying snakes in tree............I remember real well, when we went south to visit our cousins and we climbed this tree, my brother & I and our Uncle Jim came out and said do you know that there are snakes in that tree. You never saw 2 kids get our of that tree so fast in your life...that was in 1950, last tree that we ever climbed.