Never too late ? My girl is 7 months now and even though she has been potty trained for ages I still say "Go Potty" when I want her to go quickly, especially late before bed when I just want her to go and then come straight back inside. I trained her by taking her out always on her leash only so I could make sure I had control over what she was doing, taking her to the grass and saying "Go Potty" and rewarding her verbally when she did it, every time. If she would try to go and do something else or grab a stick I would correct her, tell her no and tell her to potty again. She understood no fun before going potty!
My girl also occasionally tried her luck wanting to get outside by perhaps tricking me into thinking she needed to relieve herself, she would bark once and stand at the garden door (her sign she needs to go), but then she would just run and grab a stick! I corrected this by again using the leash, saying "go potty" and if she didn't go in a reasonable time I would take her straight back inside. I think she understands potty time and play time are different now, and she gets no fun by pretending she needs to pee! Hope that helps ?