I don't know how someone can accidently pound a pet when it has a pop up asking are you sure, and none of the buttons near that pound button does the same thing besides the SPSB. Also having that option now to adopt back the pet if a brain fart happens or someone just wants something to whine about nearly makes this idea unuseful unless more is built onto it.
Nightingale, what I do is write down pairings I like for that pet on the pet's profile with a link to the other pets or the ID number of the other pets. Usually with a short description for each ID number.
So, for your idea and who has commented so far, say there is a box next to their name or a seperate area with a drop down box of all pets are to be clicked for favoriting. Once favorited, the SPSB, Pound, and possibly trades button would be faded out, unclickable as if the pet were busy? And if someone went to make an offer for that pet, those options would be faded out, making a pretty huge hint to not contact the owner about purchasing the pet. Could also say not for sale in the pet's description, but I guess not many people look at or use that feature as much as I do.
Hrm, could make a seperate area completly (maybe under account) to have the list of your own and other people's pets that have been favorited? Especially if it has the name linked, and a short description able to be written if wanted.
This idea has much potential if implicated nicely.