This sounds a lot like my new rescue puppy Puma that we got about 1 1/2 months ago. She is 5 months old and came to us with some resource guarding issues and a few other issues. She is doing so much better but of course she is young and we still have more work to do....
She too has just discovered digging in our yard this week after I had her "help" me pull weeds! I tossed her the weeds as I pulled them out of the ground and she so happily went after them in true puppy fascination, tossing them about! But now she is digging in the ground to find roots to pull up on her own. Who would have figured?
Anyway, so she is a bit growley when I ask her to stop doing her new job. And she too is sometimes unhappy about being picked up. So for the digging, I have been gently telling her no, and then trading her for some treats or I bring her one of her bones to chew on, or I throw her a ball etc. In other words I get her to do something else that is positive.
As for picking her up, we have been teaching her the phrase "pick up" and we say it in a light, fun, happy manner and then pick her up and feed her yummy food while carrying her. Or we do a quick pick up with the cue and then pay as soon as we put her down. Teaching her that it is always a good thing when we pick her up.
And as far as the plopping down on a walk and refusing to get up. Yup, she is doing that now sometimes. But for us she is doing it in the middle of my store's parking lot, right in the path of cars. Yikes! (I did tons of working with her on "relax" outside in our parking lot so this is why she feels comfortable to plop and chill anywhere)
But she doesn't understand that the parking lot roadway is dangerous. So you betcha I use food to make her want to follow me anywhere and at any time. If it works, it works. I don't work for zero paycheck, so I am more than happy to teach with food (and praise) if she learns so much faster what is safe and desirable. You can't tie a dog up and wait like some folks have suggested here if you happen to find yourself in the middle of a road
Just my take. I personally am a huge proponent of using food (and praise) as positive reinforcement. Having studied nonstop about dog behavior and learning methodology.... and having worked for the last three years intensely with my other dog Gracie who is a shy/fearful/cautious dog I learned that sometimes high value food is a super important way to change the mindset of a dog like my Gracie. Praise alone does not generally do it for these types of dogs. My personal motto regarding dogs: Change the mindset and the great behavior will follow.