I think it is a tough call. If you were on private property, with out a visible open container, then I don't think the cop can get you.

If it were me, I'd ask the cop to see his warrant or written complaint, then ask him to leave. Any word out of his mouth besides goodbye, I'd tell him I need my lawyer present, and dial him up on my cell phone. After he left, I'd sit down to write a letter to whoever the top cop in the state is; county, state and federal representatives and Governor. I'd email it to my lawyer, have him out it on his letter head and mail it out.

I have no need for the immediate satisfaction of an argument that will land me a disorderly persons fine. I'll be better served by the letter that will be in his file his entire career, and be brought up during every review for a raise or promotion he attempts to get.

If he was persistent, I'd refuse the sobriety tests and the breathalyzer.

Fake lawyers feel free to advise and pick it apart.

Edit: Really though, everyone knows it is better to mow your lawn stoned than drunk. Sometimes if I do my entire property, and the lawn mower is running really rough, I'll see trails for a while after I'm done I wish I knew a way to induce a full scale flashback. You just can't find acid like you used to.