Playing AK when the flop misses

[fluffhead]

How's it going...I guess I"l start with a hand - 1/2 at paradise. I'm on the button with AKo, one to my right open raises, I three bet, blinds fold and raiser calls.

Flop comes 7TJ rainbow - he checks, I bet, he calls.
Turn is a 9 - he checks again, I bet he calls
River is a 6 - he checks, I check behind.

He turns over A7o to win the pot.

Now, against most of the softer players at the lower limit games, do I keep ramming this or do I check it down and limit my losses? On one hand, heads up, the pot's pretty small and throwing in two big bets against a calling station who may have a pair won't win you much. On another hand, I want to play more aggressively.

opinions? Thanks in advance