How many times can I raise in a live game?

[leomerr]

A few weeks ago, I was playing 6/12 limit hold em at the Borgata. I rivered quads, and my opponent hits aces full. Being new to live play, and a long time internet player,I naturally just called his four-bet on the river. He says I could have raise him again. Could someone help me out as to how many raises are allowed before the betting is capped.