if its a roll pin you need a new one. if not tap the pin in and apply a very teeny tiny eensy bit of blue loctite to the end of the pin when it is flush in place and let it sit overnite. shouldnt shoot loose but it should hold till you need to tap it out.
more permanent you can peen it in but that will mark up the sight a bit and be a lot harder to remove
"Gun control: The theory that a woman found dead in an alley, raped and strangled with her panty hose, is somehow morally superior to a woman explaining to police how her attacker got that fatal bullet wound." L. Neil Smith
The problem with being stupid is you cannot simply decide to stop doing dumb things...
"I crapped my pants to avoid the draft!!" -Ted Nugent