7 year old dog weeing inside

[Scoobydoobydoo]

Hi,
Looking for some advice please!
We have been looking after a 7 year old male dog couple of days a week for the past few months.
He has recently started to wee inside on the living room carpet.
The owner says he is fine at hers and also at the other family who look after him part week.

Sorry pressed too soon!
Its happened twice so far. One was last week and one today. I have subsequently got enzyme cleaner and cleaned last week's spot.
Apart from taking him to the garden more is there anything else I should be doing.
We are novice dog people so any tips would be great
Thank you!