Potty issues... marking?? UTI??

OK - my first (of hopefully few) questions...

It's been a little over a week now since Riley joined us and the potty training is going a bit slower than I hoped (or remembered from Molly!!). He's just about 12 weeks old.  Over the weekend, he started what seems like "marking" - he goes just a drop on the carpet and was doing it out on the deck every few minutes yesterday!

His crate is dry though - if it was a UTI wouldn't he do this in his crate too? He's been staying dry in his crate at night (8 hours) and during the day (about 3 hours max) since Day 1.

Molly (our 18month old) is most definitely being more dominant than him in play and food. Could he be trying to establish some dominance by peeing around the house???

What do we do?
Thanks!