How do I get a new key-less entry fob for my car?

My dog chewed my key-less entry fob for my VW Pat. I saw some "uncut" ones on ebay, but I'm not sure how this works. If I buy an uncut one, can a locksmith use my old key as a model to duplicate on the new uncut one? If so, how do I program the key-less part to lock/ unlock my car?