I think the odds of getting caught by le at a MP are fairly low if that's all you're worried about.
That said, you have to ask yourself why you want to go to the MP. Is it because your wife gives you sex every day, and now she is away for a weekend and you can't make it through 2 days without sexual gratification? If so, your excuse if she finds out can be "Honey, I love having sex with you so much that I was going crazy when you went away for the weekend, so I went to an MP and closed my eyes and thought of you. I knew you wouldn't want me to suffer all weekend, so I did it for you, honestly. Now that you're back, I won't go to the MP - until you go away again and I'm alone." Yes, that was supposed to be funny.
If, however, your desire to go to the MP is that you want to try a new girl for some variety in your sex life, and your wife going away just gives you the opportunity to dabble, then go for it and either A) get it out of your system or B) welcome to the hobby - you'll be in the Hotel California (Strongbeau's metaphor - and a good one), probably for life. If you get hooked you'll need to find a way to set aside some cash to pay for the ongoing secret life.
As far as it goes, some people believe in the sliding scale whereas such and such counts as sex and this other thing doesn't. Bill Clinton is an example: BBBJ-COD (cum on dress lol) doesn't count, digits with a cigar doesn't count, etc. Only FS with the 'sword in the sheath' so to speak "counts". I myself believe that anything involving a girl physically giving you a happy ending counts as sex. I don't care if it is a HJ, bodyslide, CBJ, BBBJ (CIM, SW), Russian, FS, Greek...if you both are naked and she gives you release, it counts as sex imho. I think most women outside the biz (esp. a wife) would agree with this definition of what counts as their husband having sex.
Still, a poll I read said that women would rather find out their husband was seeing an SP then find out he was having an affair with a girl at the office. Probably due to the fact that she knows the SP isn't going to run off with him and it is just sex for cash, whereas an affair would indicate he was looking to replace her.
Get the massage if you want it. If found out say you went to a holistic health centre spa to find your inner self, and you did (all over the MPA's stomach and the towel, but don't say that) and you are happy to be in Zen like state of total relaxation. Say you would never dream of leaving her, and learned new ways to pleasure her, which was the main reason for you going. Girls go to spas, so you went to a spa. It is true - my dates always compliment me on my massage skills - skills I picked up by going to high-end MPs for years.