Yes. The kicker with tails is that they normally lick off whatever you put on it. One of the better topicals is "Cut and Heal". It has a bad taste and a lot of dogs will leave it be, although I have had a few that would lick it like ketchup. But so it goes.

Without seeing the set up I am going to guess he is banging his tail on something. Maybe something has his attention that the only way he can see it is positioning himself at an angle that leaves his tail up against the wall/fence? Maybe when he hears you coming?

Hopefully you can get it figured out. Tail splatter is tough.

My son slammed out screen door on the tip of a Fila Brasileiro once and pinched off the tip of his tail. He yelped in pain but ran down the hall way playing with my son. Then back up the hall way and into the kitchen when my wife noticed the spray and splatter. The hall way looked like a murder scene. We did everything we could and it tooks weeks/months to heal. Any tail wag and it busted back open.

Again best of luck.

EWO