Quite frankly, the DM is capable of being as much of an ass as the players. Hence, if he doesn't understand a rule, and misrules it, it's up to the players to correct him, and furthermore, it's his job to pay attention, and occasionally admit that he's wrong.
In this case the DM was flat-out wrong. I would suggest that if he persists with this ruling, then you abuse the living daylights out of the spell 'snare', which will, by my measure, completely immobilises any creature which steps on it with no save, and since they cannot take any actions, they will never be able to escape from it by the two methods specifically mentioned in the spell. This is because, at one stage, the spell refers to a creature hit by the spell as 'trapped'. My, what a wonderful third level spell that can basically kill any creature without a save or SR...
