AK/AQ.....YOU HIT THE FLOP......FOLD?

[MickeyWins]

I apoligize if this question has already been beaten to death here. Its a general question...there is no specific hand here.
my question is....

YOU SHOULD FOLD ONE PAIR TO RESISTANCE WHEN?

1) you have AK hit a K on flop...bet out,,,get called.
bet slightly more on turn...get raised...good idea to fold?

2) you have AK hit a A...get called.....
assuming no draws...HE HAS A SET?( a bad ace would raise?)
with draws on the board...you bet again...get called again.
a) should we check river?
b) he can beat the ace on board....?
c) how does depth of stack affect our decision?
(ex. M=10 or less....all the chips go in...more ...maybe we can get way from it??)

this comes up all the time in NL.....its basic....yet...complicated.
I realize...playing the player is envolved here.

any thoughts are apreciated...ty