What would worry me about it is the prospect of someone's little grandchild doing a bit of amateur gardening in the flowerbeds and digging up a chunk of decomposing pooch. Come to that, whoever does the gardening normally could get a bit of a nasty experience.
There is a good reason for the regulations concerning where burials (human and animal) can take place. Hygiene and aesthetics both come into it. In your own garden, where you know the location of the pet grave, you can avoid cultivating there, but when the garden is shared by many people, and those people could change at any time, it doesn't seem to me to be fair to do this. A pet cremation and the ashes put into a planter with a shrub would be better - or perhaps they could be scattered somewhere wild where the dog liked to go for a walk..