I have a fifteen year old sheltie and lately she has begun to urinate in the house. She goes outside but the moment she comes back in the house she urinates. They are very large puddles. She doesn't seem to even realize that she is doing something wrong but I don't know what to do. Please help

I would think that the first thing in order is a trip to the vet.

Elderly dogs who urinate in the house is a sign of diabetes.. any other symptoms? Is she drinking water more frequently?

I agree on the vet visit, she may have UT blockage and she tries, but it doesn't come out until its too late. Also there might be a problem such as something outside that is bothering her, strange dogs around, grass too high, something that just happened recently. If there's nothing like that wrong, and the vet gives her a good check then I would say she is just getting old and a bit senile. Old age can cause several problems for animals.

Sounds like a UTI.

My advice is to take a urine sample and make an appointment with the vet... good luck