This looks like some mushroom of the Polyporales Order, possibly of the Polyporaceae Family. The one in your friends garden probably sprouts on the dead roots or buried a trunk.
It could be this one Lenzites Betulina.
(credits to floraitaliae.actaplantarum)
(btw, if you do a close-up of your picture, google image search knows it's a mushroom, and shows many polyporales but don't have the right one yet...)
For your dog:
polyporales are rarely poisonous, so small intake should be harmless for a dog.
But this kind of mushroom can be very difficult to digest, which can be harmful to a dog that eat the whole thing. But never seen or heard of a dog eating mushrooms. They'd rather go to dead stuff with interesting smell than that.
If your dog takes too much interest in the thing and start eating it, then a possibility is to put a big concrete flower pot over it.