The best way to sex them is gonna piss him/her off...
The simplest method is to invade their privacy and look under their tail. On the underside of their tail, just above the vent, there is typically either a single bulge (or none) or two separated bulges. If you see two clearly separate bulges, you have a male. If you see only one, you probably have a female. There is uncertainty with a single bulge, particularly if there isn't much of one. When beardies are young, they all look like females, but develop clearer signs of gender as they get older. You should be able to tell by time they're 7-8" STL. The best way to hold your dragon when making this check is to place your dragon in one hand, perpendicular to your fingers, and facing away from you. Place your thumb over the back to hold them in place. With your other hand lift the tail up to approximately 90 degrees. Be gentle!!! You don't want to hurt your beardie.
And i second the substrate being a bad idea...slate tile or repti-carpet is a much better, safer, and easier to clean idea
