My buns love to test the boundaries! They will nibble books, pick up anything on the floor, my female bun comes into the kitchen when I cook and runs off with scraps I drop! Im surprised she hasnt died yet with the variety of diet she gets
Make sure there are no places they can get stuck, but enough safe spaces for them to hide and run (ie carpet instead of wood floors). Mine love it under the couch and it is just a cheap ikea couch so I dont mind her chewing the wood underneath. I have learnt to distinguish what she is chewing on by the sound of it haha. My male doesnt have front teeth so he never tries to reconstruct the house but the female does and I have found its better to re-direct her to areas she is allowed to chew rather than abolish it all together. I have some thin planks of wood protecting the skirting boards as she has had a nibble on these before. She also knows how to open doors – dont let the buns ever learn this in the first place! LOL. The male is still new to the family and much dumber in the head, so he is barely any trouble but my smarty female bun is very much the explorer and adventurer and I needed to make a fair few adjustments to make the home safe for her. She would jump up on my bed which was over a metre high! And then JUMP OFF IT! I was terrified she would break her neck even though she appeared to enjoy this and do it with ease. I have made a wood floor “buffer zone” around the high areas, she is smart enough to know the floor is too slippy for her to launch herself off. She cant even jump on the couch now thankfully as I always leave my dinner plates there!
Mine have their “bedroom” pen for at night and when I am not home, it has ample space for them both and they could live in this full time but they just love the freedom and snuggles in front of the tv at night.
My best advice is dont train them so much that they become too smart for their own good!