I'm kind of late to this party, but my advice would be to not do it. Most guys I know who fuck around, don't give it a second thought. They hit up the target, get what they want, and then move on. Their girlfriends might be suspecious, but they know better than to ask too many questions. Women know that what they don't know won't hurt them.
I went bar hopping with a recently married guy. A young guy. We entered what many would call a "cougar" bar. As we entered the bar, immediately, a couple of older ladies approached us. To make a long story short, both my friend and I took the ladies back to my pad. In between initially meeting the ladies and taking them back home, my married friend made a HUGE deal about not wanting to cheat, and loving his wife, blah, blah blah. I found it all too funny. To me, it realy is not that big of a deal. The woman only wanted to have sex, nothing more than that. Throughout the night, he was actively trying to convince me to leave my girl, so he could get away from his. I didn't care either way, but whenever I was ready to bounce, he would be on the sofa kissing the girl. Like i said earlier, he eventually ended up having sex with the girl on my couch (yeah, real nasty!).
At the end, we dropped the girls home, and then his whole demeanor started to change. He was back to the whole, i love my wife and what did i do routine. He left my apartment without taking a shower or washing his clothing (I would have let him do both). What is worse, apparently, he bruised his penis when he was unzipping his pants. So he went home smelling like another woman, with a bruised dick and a guilty conscious. I have not talked to him in two weeks, but I would not be surprised if he told his wife.
As for me, well, I have a girl that I am "kind of" seeing. I wouldn't be surprised or angry if she was sleeping with another man. If I ever get married, like all the other men in my family, I'd probably be open to some auxillary trim.