Nah, you won't have to fight him for it, he's probably marked you too!
Besides head-rubbing, gliders will also "chest rub" and "booty dance." It's difficult to see them do it while they're perched on your shoulder (unless you have a mirror), but if you notice him doing what looks like a sexy push-up (where he stretches his arms up, and then moves his chest forward while dipping down to rub it on you) that's scent marking as well. :) The "booty dance" is sort of exactly what it sounds like: he might scoot his back end side to side while tracing a faint zig-zag trail with his cloaca. Even my neutered male does this! :)
Anyway, I hope now you can catch him marking you, because there's nothing better that realizing your glider is saying "I love you!" and claiming you as his own!