I taped it on the back and 2 sides from the bottom up to high enough that he couldn't see over. If you put it on the outside, it will make it more reflective, I think, so if you decide to try this, make sure to put it on the inside. My beardie never seemed bothered by his reflection, and then when he was about 10 months old, he stopped eating. The vet couldn't figure out what was wrong and I had to syringe-feed him for about 3 months. One day while he was running around on the floor, I noticed him charge his reflection in the glass of the wine fridge and so I covered up the walls of his cage. Two days later, he started eating again. Now he's fat and I'm trying to get him to lose weight.
Anyway, it's just an idea that is fairly easy to try. I think when they become sexually mature the reflections can bother them more because they think it's another beardie.
It's good to get fecal tests done every so often, I think every six months is what's recommended.
Beardeddragon.co does a fecal by mail for $10. I've never used the service before, but I've heard positive things from others.