the best way to punt without getting caught is to know your misses schedule, than work with that, don't make any excuses to go out without her when its suppose to be your time together, also encourage her to go out with her GFs for some retail therapy at least every second weekend, so she has her own quality time away from you, so she won't get suspicious of you doing the same.
On Holidays i recommend you book her a day Spa package that takes up a few hours so she can relax, than you can dash off for a punt.