Locking in the rear sight

[uptime]

Now that I have zeroed in the sights on two rifles, how do I keep the rear sight from being accidently knocked out of alignment? In both cases, the rear sight fits in a dovetail and is moved left or right by tapping them with a small tool. Except for the tight fit, there is nothing to keep them in place. Can I use a bit of clear fingernail polish to help hold them in place or is there something better to use?