hey guys, I'm done lurking, so here we go..
A little background, I'm usually fairly tight (VPIP 21%)and probably average aggressive. Been experimenting with a more laggy style, so I've seen more than my average share of pots when this hand came up. No good reads on villian, haven't seen him get out of line this session. In the past he hasn't been a superstar or anything.

.5/1
UTG (villian)(49.5) limps, hero UTG+1 (Ad Ks)raises to 5. All fold to villian who calls.
Flop Kh 5c Ad
villian checks, hero bets 8, villian calls
Turn 3h
check, hero bets 15, villian calls
river Qs
villian checks, hero checks behind..

My question is this. I feel that I'm probably losing alot of value by checking behind on hands like this, but the smooth calls make me a little edgy. I guess I get a little worried that if I bet again I'm exposing myself to the possibility of someone coming over the top and putting me to a tough decision. (I know it doesn't matter here as much since the villian was short stacked, but if his stack was larger I get worried about committing my stack to a 2 pair type of hand) So my question is this- what kind of guidelines do you guys use when deciding to value bet your hand on the end, and how often do you back your bet up with your stack if someone comes over the top? What kind of hands will you defend? (Top two or higher, sets or higher, etc)
(i'm sorry if the question is a little vague, I'm sure it depends on reads and the like, but any guidance appreciated)

It would be very hard for me to believe he has you beat here. Someone with a set will almost always raise the flop or turn. As a matter of fact, I can only remember 1 hand out of the 10s of thousands that I play where someone just called me down all the way with a set (in a pot that was raised preflop).

I would say 25% of the time they raise the flop and 75% raise the turn. So, he doesnt have a set.

Unless he has 24 or JT, he doesnt have a straight. I think he has something like AJ. he could have KQ, but even then he might lead push all in at the river.

The pot is $57 or so and he has $21 left. I put him all in. He cant bluff raise you, he doesnt have enough money left.

You have top two and someone is just calling you down and only 55 or JT are likely able to beat you. You shouldn't worry about a tough decision at this point and either win the money or lose the pot.

My criteria for value betting even with a one pair hand is, if they are just calling, I'm still betting, if the turn or river was raised there are arguments to checking it down or folding when you were raised. Value betting, especially if you are known to be a lag with top two is essential, you really do have a hand this time!