We just came back from a trip to Lake Tahoe. Marley had a blast swimming and hiking...but I just noticed a huge sore under his arm. I think it could be from wearing his harness the entire time. He just gets so excited and is easier to control when he is wearing a harness. I put some neosporin on it. Should I be concerned? There is only one sore that I can find on him. Should I take him to the vet? Here is a picture. Thanks for any help.