I am in the same situation. My neighbor also allows her large dog to roam free. And not only does he poop in my yard and gardens but he also rolls around and sometimes sleeps in my garden beds. I put a lot of time and money into these garden beds so I find this quite frustrating. But I also have seen and heard enough of her aggressive behavior to feel unsafe about trying to approach her.
To make matters worse, a small child member of her family has been coming into my yard and leaving my gate open so that a couple times my own dog got out of my fenced in yard. I have had to lock my gate which is frustrating, because now I have to inllock and relock every time I come and go from my own yard.
I am so shocked that in such a relatively nice neighborhood so many people fail to curb their dogs, and or clean up after them. It's a fairly routine experience for me to find huge piles of dog poop in my yard.
As for a suggestion? I called animal control and they said they wouldn't come out unless I had the "stray" animal in my custody. They suggested I trap the dog in my garage or shed. Only then would they come out and do something about it.