water bottle

[Elmer]

Hey,
Two of my female gerbils have become very restless lately! I give them
plenty of attention, but in the last week they've gone through TWO water
bottles!! What to do? The first one was a 8oz bottle hanging from the
tank w/ a metal guard, (they preceded to jump up onto it and chew the
top off) and the other was a 5 or 6 oz Quick Quench. Any suggestions?
-Esther