There isnt anything holding them on other than friction.
If a sight is already in a dovetail you can safely use a delrin punch brass punch or wood dowel todrift it.
If its all the way out or falls out at some point you need to use a sight drift tool to install it. If yours is really loose one teensy eensy bit of rocksett or blue locktite will keep it still. You dont want to do that unless its loose and keeps shifting.
"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