Our 13 year old dog cant help peeing every where ,had him to vets and all tests came back fine?

Vet did a water test that was fine no infection also did a blood test he did find i think he said a high reading to do with his liver but said it was only marginally high not to worry to much .Why is he peeing all the time ,vet suggested he may be going senile ,im letting him out hes having a pee outside then coming in and doing it on floor .He also walks & pees i dont think he knows hes doing it .could there be any other medical explanation ? he also sleeps alot