You are only playing with your stack size. That is, you can only lose what you bring to the table.
Them having three times as many chips in a ring game is the same as if they have an equal number of chips as you.
If they are betting too high for the stakes you are playing, then tighten up and punish them with your big hands.
If you are playing with a stack too small for the stakes you are playing, then either move down in limits or buy in with more money.
You should only be playing with a stack that you are comfortable with losing, and one you can rebuy if you happen to lose it.