It's 3 mirrored surfaces at right angles, yes. However the purpose is to reflect the light back where it came from, and if you want to do that accurately over a significant distance the right angles have to be very precise.
Say the laser-toting miscreant is 100m away and you want to direct the beam back onto the hand holding the laser. For that you'll need the right angles to be correct to within around 0.05°. You're not going to do that by gluing mirrors together by hand. (That isn't to say that you couldn't make a useful one by hand, depending what you're trying to achieve. Just illustrating the precision calculation.)
The expensive prism reflectors gp linked are even more precise than that. They say 3 arcseconds, which is less than 0.001°.
There are corner reflectors placed on the moon for precisely measuring the distance to it. I bet those are really precise ones.
Also from the perspective of engineering, if I wanted to DIY an accurate corner reflector cheap then I'd use the property of returning laser beams to their origin over distance to do it. Make a jig to hold the three mirrors, make sure they can be fixed to the jig firmly and glue them up. Test the ability to return a laser over distance. Calculate (somehow...?) the error in the jig, adjust it, rinse and repeat.
Another idea for a far cheaper way to turn the tables: create some fine mist or dust in the air near the dot so that you can see the beam then take a picture, or even better a video where you move around a bit to create proper perspective. Then you or authorities should be able to better identify where the beam originated.
I think they’d need to be first-surface mirrors. Here are some 94% reflective acrylic mirrors. They are not outlandishly expensive. The high end glass ones are, though.
