If you have KK to a Kh xh x flop, and someone has xhxh, they have 7 outs (9 remaining hearts, but 2 of which can pair the board, leaving them 7). That gives them a 30% chance to hit the winning flush by the river, or 2.3 to 1 odds. So, you must take this into account in your betting. In this case, I bet the size of the pot. He does still have pot odds to hit the flush by the river with this bet, but not on the turn. If the turn blanks, he has 7 outs, or 15% chance of hitting the flush. He is about 6-1 to hit the winning flush now. So, when you make a bet this time, you just have to make sure he is not getting 6-1 odds to call (not hard to do). If he calls with bad odds and hits, oh well, you still played your hand correctly, you know how he plays, have notes on him, and can take advantage of his play later.