Unless you have a warrant signed by a judge. Then you can shove a recording device up the guys ass and record his conversation with his own mom.
Then you can also turn it into the issue of infidelity. With the generally approved theory being all bets are off. That means a private investigator could record you and follow you around to see if you are having an affair, cheating you business partner out of money, scamming an insurance company and so on.