Margaret - Extension does not recommend using sealers, as they tend to actually inhibit the tree from healing itself. Keep the tree as healthy as possible, reduce stress, and the tree will form its own scar tissue to block out rot and insects. Here is a link for dealing with mature trees: http://www.treesaregood.com/treecare/mature_care.aspx
. I would advise against rope, because it will hold moisture against the bark and eventually has the potential to strangle the tree!