Taught my dog to smell a clothing item, and she can distinguish the right person and follow the footfalls that person walked. She is pretty reliable up to about 18-36 hours old depending on weather conditions.
Just about any dog can do it, as long as you can find a good reward system for the dog. Mine loves playing fetch, so once we find the person we're looking for, that person gives her lots of attention and fetch play.
It took a lot of work, and a lot of help from other people, but she's really good at it now.
I don't personally have a dog but I taught a roommate's dog to drop the ball by dropping a piece of chicken breast when he was looking up with the ball in his mouth and saying "drop it or drobbit!" as it descended. Then he dropped the ball and learned its more fun to drop it!
One knows paw. The other knows sit. They do it if they feel like it. So it's more about if they want to indulge us or not. They will return to whistle which is useful
Technically I taught my cat this first but dogs can be persuaded to allow you to pet them and rest your foot on them so you can lay at a distance and still have contact and like pet/groom them with ur totally clean feet 😽
Just watch out for foot cramps 🙀 They are ![excellent]