I just realized (thus my edit) that they are hiring you to act as a bodyguard for the wife. If they are paying you up front and you will have collected the funds before doing the bodyguard work, I don't see the problem. Since you see a problem, I'm probably not understanding the details.
Checks will take at least 10 business days to be fully "cleared." Your bank will let you have access to the money usually after only a few days, but a counterfeit check could still bounce two weeks later. Releasing the funds is not the same thing as the check clearing the bank. You are at risk until it "clears."
So if they wire the funds, those should be good funds and not reversible. if they send a check, don't perform the services until the funds are actually clear. I assume this is someone purportedly overseas, so any check would not be drawn on a bank you can pick up the phone and call to find out if the check is good, or take it to their branch and cash it on the spot.
Time to build a bigger bridge.