Lived here ~25 years, bought the house March 2000. Soon afterward met a
neighbor who shares a fence with me. We live on cross streets, and my
back fence is his left-side fence, partly. My entire back fence is the
back portion of his left fence.

He's had dogs ever since I've owned the house (i.e. at least 7 years).
If one of his dogs dies, he gets another. We introduced ourselves and in
an effort to seem quite neighborly he offered to lend me tools any time
I need them, should I need them. I've never taken him up on that... I
have a lot of tools and when I don't have some I need but not enough to
buy, I can generally get them at the very local tool lending library
(Berkeley, CA). Under the current circumstances, I would never dream of
asking to borrow a tool:

His dogs' barking has sometimes bothered me a lot but that's not the
subject of this post. The dogs crap a ton just over my back fence, which
is on the left side of the garage my neighbor built a few years ago. It
seems like he never cleans it up. AFAIK, he's NEVER cleaned any of it
up. If I'm near that back fence, I can smell the crap. In the summer
(i.e. now), the smell is so bad I can smell it most times any time I go
in the back yard. Glancing over the fence (wood fence) a couple of days
ago I saw (didn't count) must have been over 100 craps.

I've never mentioned this to anyone except a home-owning friend of mine,
who himself owns two dogs. His reaction is that it's terrible and
"unsanitary." Now, this friend of mine has a history of occasional
serious conflicts with his neighbors, serious enough that he sold his
house and moved into his other house (he buys fixer-uppers and now makes
a living renovating them). I always try to avoid confrontations with my
neighbors. I have enough to concern me without second guessing how I'm
getting along with them, worrying about what they think about me, etc.
I'm wondering if I should or can do a damn thing about the dog crap.
Yeah, I could politely talk to my neighbor, but I don't know what
footing I'm on here. Is this guy required to clean up after the dogs?

TIA for wisdom, etc.

Dan