I used to just set them up with an obvious enclosure design which made it obvious where they'd want to lay their eggs, and I put nesting substrate there. Countless clutches over the year, not a single egg laid outside the nesting area, every fertile egg I ever had hatched and it wasn't until the last season I was breeding them that I had my first slug. You can add lots of things for them to climb and explore in if you like, but keep it thermally simple and obvious (one single heat source right up one end of a long enclosure is easiest and most obvious) and they'll always want to lay under the heat source (may not always be true for large monitors, but it'll work for stuff like Ackies and pilbarensis without fail if you set it up right). A well designed nesting area in that location and you'll be fine. I buried spaced tiles in a mixture of vermiculite and red desert sand (there are plenty of other options, but that's what I first used and I just kept going with it), they'd dig out a burrow beneath a tile (if you use this method make sure the tiles can't collapse when they dig out the substrate) and lay in there. They'd spent a lot of time burrowing in the days before laying their eggs and often hang out in the burrow where they'd lay their eggs.
I learned about where they'd want to lay their eggs from breeding dragons. At first I used to lose dragon eggs because I'd put the nesting box in a good place, and the lizards kept choosing to lay them right until the spotlight which would kill them within a few minutes. So, I started putting a nest box right under the spotlight and they used it every time. I adapted the design for monitors and used my own personal tweaks to the design, everyone likes to do it a bit differently, but that's the overall gist of it.
