So maybe if you gave a run down of where you're getting stuck, you could get options (both +R focused and otherwise) that could help.
One from this morning's walk.
I take Millie past our little local shopping centre to get her used to automatic doors, cars and people. It's only 7am so there's not many cars or people so I can stack the cards in my favour.
As we crossed the road to the car park that runs around the perimeter of the shopping centre we were coming up to a plastic bag. Rather than totally avoid it I try and use opportunities like this for training, like most people I suspect. As we approached I gave the command "leave it". Now Millie is 8 months 10 days old so we've worked with "leave it" for 6 months, there are no questions that she knows what it means and in various situations. Despite that she still stopped and dived in to the bag. What she came up with was the leftovers of a Subway sandwich. Completely blew off my command.
Reading her face and body language I knew she didn't want to give it up, and that if she wasn't on lead she would run. "Drop" had nil effect. I had fresh chicken breast on me, we are working on loose walking and focus, and swap was ignored. I ended up having to pry her jaws open to retrieve the bread. After doing so I offered her the chicken again and she refused. Again, reading her told me that she had more so in I went again.
The night before hand she swallowed something whilst I was asking for a swap/leave it.
I'm glad that neither the Subway nor what she had swallowed the night before were toxic. But it concerns me that she has the confidence to disobey "leave it".