Bricks or abrasive structures in the enclosure are a good way to keep the nails filed, but I understand that it isn't always practical given a your setup to use more rigid structures.

You can use nail clippers meant for humans or small animals - Look at the bearded dragon's nail and you should see the 'quick' on the underside, closest to his extremity. The nail should be black in color (unless your beardie has clear nails) and the quick will appear to more of a fleshy/brown color. This is cakewalk to explain with pictures, but I understand it may be hard to follow in words.

Anyway - get yourself a little pile of flour or corn starch. Cut the black NAIL tip, but do not cut into the quick (the hyponychium contains living vascular tissue and will bleed if cut). If it you do nip the quick and it bleeds a little, it isn't the end of the world. Simply dip the toe into the corn starch or flour and it should stop pretty quickly. Thats what I've heard at least, never have cut the quick on mine yet *knock on wood*

In essence, you are simply trying to trim off just the tiny tip of the black nail that is sharp.

Nail on top (represented by "-), Quick on bottom of nail (represented by "."):

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There is no benefit or harm done to the animal by trimming its toe-nails. Purely for your benefit to prevent being scratched quite as much = )