How do I deal with my mother in-law?

I realize that I may be asking a very vague question here, considering the variety of issues that women have with their mothers in law... but at the same time, I think it all stems from the same place... the refusal of a mother to stop interfering in the life of her child... She keeps interfering in our lives and at the moment it is affecting our relationship.
I fear I may always be on the losing side of this battle, because I am not willing to stoop to the same levels of manipulation that she does. It's all too easy for her to start crying and play on his emotions, which she does, and he is left giving up more and more ground. I, on the other hand, am not willing to emotionally manipulate or silence him - meaning that every time concessions are made, they are in her favor.
At this point I am afraid of losing him or even losing myself due to constantly having to give ground. How do I deal with this situation? I really don't know anymore