Hm, Deefer's a bit passe now - everyone knows the joke.
How about Fleet, Tag, Cap, Sweep, Glen?
From the International Sheepdog Society
"The Society permits the use of only one, simple working name for a registered dog. Working on the fields, perhaps with more than one dog, a shepherd will be able to cope with names such as "Ben", "Meg", "Cap" or "Moss". But imagine trying to work with "Philip", "Flossie","Pretty Boy", etc.
We are quite happy to accept non-English language names. The test is that the names should, ideally, be single-syllable."