it's very difficult to attach a mini to an actual rock. A better option is to either use wood chip/cork chips (like you get at garden centres for putting around pot plants*) and just paint it to look like a rock, OR you can take an actual rock, with a nice flat top, attach it to a base (using superglue or whatever), texture the base with sand, smaller rocks, etc, and then cast the whole thing using resin. This allows you to then drill holes in the resin to pin the miniature's feet to the base.
*that's plants in a pot. Not any other kind of pot plants you may be thinking of...