You cant just grab any female dog and expect to fuck it. Dogs, even large ones are too small for human cock. Yes I know you've seen porn where some guy has is dick in a chihuahua. what you don't know, or notice is something that small has probably had puppies recently. That greatly stretches them out. I've been an active zoo for 35 years. I've never had a female dog I could have sex with, without special circumstances. The best and easiest is if she has had puppies. A couple of litters and she will permanently be loose enough for you. Or, with a lot of time and work over the course of a year you can slowly stretch with toys. Aside from that. Every husky or german shepherd I've had has been too small.
And please, if you want to be with a dog do it with your own. Dont go trying to fuck your friends dog or some other random persons dog. Things like that and getting caught gives us all a bad name and makes it harder for zoo lifestyle to be accepted by non zoos.