(elementary) standard line when scare card hits river?

[cbloom]

I feel like I'm losing a lot of money on this really common situation :

I have something like a decent top pair OOP, I'm leading the betting the whole way, about 2/3 pot. On the river my nightmare card hits - the flush makes it or whatever. What do I do?

My standard line on this has been to bet about 1/3 to 1/4 pot, but against aggressive players, that just screams "top pair, please don't bluff me!", and they will oblige and come ott and it's hard to call. The little bet is just giving away money.

How do I decide to check-call or even check-fold ? This is at party 6-max so I'll often see lower top pairs or even middle pairs here, so just folding the scare card seems much too weak.