If you are really serious about this, I would recommend buying a nice pair of clippers, not cheap ones. Cheap ones are not worth the money IMO, especially since you have a cocker and they have thick fur. I would recommend getting one that has removable blades. If you get the ones with just one blade that doesn't come off to cut the fur longer you have to use the snap-on combs, which do not compare to using a longer blade. They often will not go through thick coats either and don't cut nearly as even in my opinion.

This is the pair that I have... http://www.petedge.com/shopping/prod...ProductID=1172
They've been in use for at least 3 years now...I bought them off a groomer who was quitting about 1 1/2 years ago. I've had to have a few things replaced, but they still work fine.

A girl I work with has this book, and I've looked through it several times http://www.petedge.com/shopping/prod...iProductID=630
It has nice illustrations and it's easy to understand. It will tell you what blade #'s to use for what. I'm sure you could find one specific to cocker spaniels though.

Grooming is not as easy as it may look!