Their's several different types of decoy strategies that you can use. The first type is sex decoy's then we'll talk about social media decoy's.
Sex Decoy's are private investigators who specialize in matters of infidelity. So, do the same thing the P.I's do. If you suspect that your partner, if given the opportunity would cheat on you, then you send in a friend that your partner does not know to create a chance meeting with your significant other to see if they would react to the decoy.
You would tell the P.I. all there is to know about the suspected cheater such as their preferences (short, tall, blonde brunette,etc,) tendencies, likes, dislikes, description, hobbies, habits, and any other data necessary.
Once you match up a decoy that fits the profile for the case and decide your approach.
Example: If your husband is a locksmith, we might have the decoy lock her keys in her car and call subject for a service call. The sex decoy will then engage in small talk and try to ask him out for being so helpful. We see if the subject takes the bait then and there, or if the subject exchanges contact information with the intention of meeting up later, given a chance. If the subject is loyal, it is likely that the decoy's advances will be politely turned down. If they take the bait, we see just how far they are willing to go with the decoy.
Make a profile on social media sites that your partner uses.
use a different name and a picture of someone that you think your partner would go for.