i know this might sound crazy, but it could be him trying to punish you for not spending time with him or giving him attention when he wants it.
my dog punishes my husband this way (for example he couldn't lay still and was put in the front room to sleep. i woke in the morning to a lovely mess and edgar just staring at me like, "and what??")
do you let him drink freely? maybe you s hould control the amount he drinks and at what times and take him out about 10m after. (i'm not saying to cut back on water, but what you save by taking him outside vs. 20 minutes of paper towels and doggy carpet odor remover...)
hope that helps.
t |