Do I bet this river?

[FoxwoodsFiend]

5/5 blinds NL at Foxwoods. UTG is a tricky aggressive player who has trouble making laydowns. He has about $9k and I have him covered. I have a TAG image and have gotten KK 3 times in the last hour. I get KK on the cut-off with 4 limpers and raise to 50, two callers including UTG. Flop is 2 4 9 rainbow. Two checks to me and I bet 250. UTG smooth-calls which is abnormal (he rarely calls, normally always jamming the pot) so I immediately put him on a flopped set. The turn comes a king and the board is still rainbow. He makes a comment like "I don't think I like that card" and checks. Now I'm sure he has a set and is worried I have KK- I bet $1000 and he calls. The river comes a 4. He checks.
I now have a serious problem with betting the river-since I put him on a set, he could easily have rivered quads here but if he has 99 I can take a decent amount off him. I'm worried about exposing myself to a check-raise here-should i bet this river and if so, how much?