Sounds like the owner of the dogs is at least willing to help put an end to it. I'd take that as a good sign.

If the spray he bought you doesn't work, then perhaps HE will do a better job of restraining them. Hopefully.

So far, though, I can't fault you for the way you've handled this so far.

I wonder if non-lethal rubber bullets would discourage the dogs and not permanently harm them... You know the old saying, "there are no bad dogs, just bad owners". Etc., etc.