I've had 5 dogs in my lifetime that have lived to age 15+. All I do is take them to the vet yearly and feed them good quality dry dog food.
I have lived in rural Arkansas to the east bay California, as far as exposure to various things. I've had a half wolf dog in AR that would routinely kill and eat armadillos, opossums, terapins, and all kinds of small wildlife. He was probably exposed to all kinds of nasty things.
Never did I give him any of these dog preventative medications that seems to be so popular today.