Sounds like our Sadie. She’ll spend hours outside with us, come back indoors, and five minutes later she’ll do the Gotta Potty Stare.
It’s our fault for not telling her to Potty before we came back inside. With her, it’s Outside Play or Outside Potty. She doesn’t combine the two.
Invite another (trained) dog to your back yard and let him pee away. Dogs have an uncontrollable urge to re-pee over another dog’s pee. This provides opportunity for you to praise, praise, praise!