I hate when the employees at the shoe store bug you. Then when I say no thanks I don't need help they practically hover over my shoulder.
Leave me alone and let me find some shoes!
I use "No thanks, I'm just browsing." It's important not to look at them when you say it. Focus on the shoes, not the person. Afterwards, they'll usually leave you alone until it's sizing time. "browsing" is open for interpretation. To me, it means "I'm probably broke and have nothing better to do." Anyways, message sent.