That is probibly the reson why he was dumped

People are so ignerant.. Anyways Yes is her neuterd?/ He is marking his territory. If he is neuterd he will not do this inside with basic trianing.. We had a dachund tha was'nt nuetered and he would pee inside all the time and it was impossible to train him.. You have to get him neutered.. good luck with your new puppy