Possible Lost Black Dog in P.Rye

If anyone has lost a dog, it might be in Peckham Rye Park. I?ve just walked past the Rye, opposite Harris Boys and a black dog ran by going the other way. It was behind the railings and on its own (although it was dark so hard to tell). The park is closed and locked up. I didn?t know what I was seeing til it was gone but it looked like a medium to large black lab, it had a collar on with round metal discs on it that were clanging together. It was headed towards Peckham.