What else could u suggest hehe interms of rocks? Hahaha
I'd suggest rocks that don't float!
Not joking, either. I once purchased about 100 pounds of a rock called Feather Rock at a quarry near my home. It's a porous, volcanic rock, similar to lava rock used in barbecues...except it's so light that most of the pieces actually floated! And if you think that wood takes a long time to become waterlogged enough to sink, well...you ain't seen nuthin' yet...
Regarding your driftwood, I don't have much puffer experience, but that wood looks like a perfect base to anchor a few Anubias plants, and/or maybe some Java Moss. Both those species actually live and grow in my tanks, so you
know that they are hardy. No idea of how the puffer would react, maybe someone could advise?