Why does it need to sound the same? Dogs will acclimate to any new name you give them IME.
but since your requirement...
hazy pear
I have a chocolate lab named Bacon. When we get our yellow lab, his/her name will be Eggs.
I have the same issue...adopting a dog this weekend, a golden retriever named 'Summer'. I need a new name! The foster people tell me she doesn't really respond to that name anyway (LOL), so I guess I can start from scratch. It needs to be cute and not human sounding (like Beth, Janet, Beatrice, ect.).
I think in most cases new owner needs to use the old name or something that sounds close.
Honey
Funny...I actually thought of that but my friends shot it down!
I think Rodent would be hilarious, but I would get too many strange looks LOL
