As our dogs get older, their little bodies may no longer work as efficient as they used to - it works the same with humans too!
The aging process may mean that he simply can't hold himself for as long as he could when he was younger.
Have you considered letting him outside more often to see if this helps?
If it doesn't, I'd take him to see his vet.
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Toilet Troubles by: Anonymous
If your cocker spaniel is normally well-behaved and there's been no real traumas in his life, ie, new member of the family, recently moved house, etc., you need to look elsewhere for the reason why he's suddenly started to poo and wee indoors.
As your cocker spaniels is in his senior years, it could be that he's experiencing problems with his 'plumbing'. I'd get him checked out by his vet just to make sure that he's ok.