Make it fresh! I made some the day before Christmas, and decided it was safe for me to eat it the day after making, so I could share in the eating of it at Christmas.

That's probably not the answer you were looking for, though. It takes a bit of time, effort, know-how and of course the right culture. I wouldn't eat any form of shop bought feta, though - deli or pre-packed. Depending on the salad, maybe you could substitute with havarti, or shaved parmesan?