[melody]

Yeah, this is very usual with older dogs. But it is still not late to teach him the proper behavior. Try reinforcing your superiority to him so he would respect when you tell him when you say no. If he respects you enough, it won't be too hard to direct him not to do it when you tug his leash when you go outside. Try also to look for some behavior issues underneath. Maybe your dog is experiencing something unusual that makes him stressed out and releases it out when he does his markings outside.