Find a very tight fitting drip tip. Usually the ones with dual o-rings fit pretty tight. These can lessen the possibility of the tank sliding off the tank.
It's still not a good enough fix if you have a habit of picking up your battery device by the tank. That's just a bad habit you need to stop.
Most of the inexpensive tanks costing less than $25 have poor fitting seals which allow the tanks to be slippy-slidey on the carto. All the higher quality pyrex tanks (IBTanked, Phiniac, etc) have very good, tight fitting seals. Once the tank has been set up for a while, these tanks hug the carto well enough that the chance of accidentally pulling the tank off of the carto is nearly impossible. This is why I feel it is worthwhile to invest in a good pyrex tank.