Rocks are abrasive and scratch your bands as you let rip.
Tbg is great performance wise but as said already they don't last long. My last set went at about 150 shots, which is about just enough for me to get used to the bandset!!!
I really like green 2050 tubing, it's cheap, reliable and consistent. Haven't had any snap on me yet, and I had around 500 shots out of my last 2050 set which snapped the pouch. It's a pain to tab them but as single tube they are about the equivalent of 20-25mm theraband singles.
For something stronger you are really looking at orange/green dub dub