Deing an 8 yr old male dog...experiences? I know its not a horse ?

At his age, he probably won't know he doesn't have his anymore. It's like when you go geld a stallion after 15 years, most of the time, they still act like a stallion. Him running off probably isn't him trying to find a mate, since it's a new area, he's probably just seeing what is around. It's new to him, give him time and he'll probably stop. If he doesn't stop, neutering is worth a try.