My mini viper does leave marks. They are slight but they are there. It is not enough that it will damage the tree, in market value or health. I do not think the damage is great enough to let any form of damaging agent into the tree. Maybe you should climb a similar type of tree that you would be climbing on their property, hardwood and or pine, and send some pictures to the land owners. Explain that the impressions in the bark are minor and that you want to make sure they are all right with it. That will show your concern for their land and abiding by there wishes. That might be enough to let them grant you permision to use the climber.