Can I use my tin cans as garden borders?

That's a great idea!! I picture it like this, keep us posted!

Dog food cans I do not think will be tall enough,once you sink them in the ground.

I am all for recycling but when it comes to tin cans I would not recommend them for use in the garden. They will rust up and become brittle and then that will become a danger in the future when you do your gardening and get cut from rusted metal, which could lead to a terrible infection. I would try to come up with an alternative idea.

Maybe you could use them as molds to make concrete edging.