20-40 flop & turn steal defense

[PokerHorse]

In my game there are a couple of regulars that when there is no raise pre flop, if its checked will bet it, of course if they are last to act or if under the gun or second, will bet out on the turn if its checked. i make this play too, but i dont try to defend enough. The bets are of a high enough frequency that i know at least aprox 50% of the time they have nothing.
I want to check raise them on the flop and raise the turn bet when they bet it, but i know that a certain percentage of the time they will have a hand, so I need help as too how often I might make this play etc.How do you guys handle it. Thanks in advance