I saw this tutorial yesterday on Pleat Week at See Kate Sew and I just knew it would make a great project for another slide-on dog collar accessory or embellishment (whatever you want to call it).
The idea is to sew pleats onto one rectangle of fabric, then sew another piece of fabric to the back so it could slide onto a headband.
I think this could easily be converted into a project for your dog's collar. Make the pleated fabric the exact same way, except slide it over the dog collar instead of over a headband and viola! You have another cute accessory for your pooch.