Hi Donna,
When adult dogs toilet indoors it can be more of a behavioural issue, rather than a dog simply not knowing the correct procedure or not being able to hold on. Scent marking is a role that dogs can take on when they feel they hold some responsibility in their home, so the first step is to clear up any confusion around that belief. Going back to basics with toilet training, proactively taking your dog out and running him through the correct procedure, is also advised. When he is indoors try to restrict his access to a smaller area of your home as you will be able to keep a closer eye on him and he is less likely to toilet in an area he spends a lot of time in.
We do cover this issue more comprehensively on my membership website….maybe take a quick look…its a $1USD trial for 3 days…All the Best, Doggy Dan