The dog owners @ my building continue to allow their dogs to urinate and defecate in the lobby and the front of the building as well which is like 100 feet of the street.

What can we do?

I posted and spoken and no one give a damn. This is no fault of the dog it the owner and/or walker.

Please suggest what can be done.

IN the lobby? That's pretty bad. It's pretty hard to stop them from urinating at the entrance however, since most dogs tend to urinate once they get outside.

You could talk to the building manager and ask that signs be put up stating that that area has been poisoned.
I know if I saw a sign that said the area had been poisoned to get rid of weeds I wouldn't take my dog anywhere near it.