Trim with pet nail trimmers. Try not to get the quick, but if you do it's not the end of the universe.

My monitors have plenty of dirt and rocks and such and their nails get hugely overgrown, even when Moggie had her outdoor enclosure with logs to climb on, mulch to dig in, rocks to lie on and turn over... her nails still got very overgrown. I cut them when they look too long, or they can and will break, which can be much worse than the "stress" of cutting the nail.

And tegus often seem to like contact and handling. My Groo used to follow me around and come climb into my lap in the outdoor cage. The monitors on the other hand.... not so much.