I zip tied mine, but even with tightening it just enough to not slip off, they're outgrowing them very quickly. 200 zip ties would be a pain in the arse to adjust or clip off and rezip. Our BR roo came from the feed store/hatchery with a blue dot on his head. Maybe you could figure something out that would be similar (shoe polish?! lol). I just don't think that P. marker is going to hold up.