Trouble with Eating - Nothing and Everything!

We have a 7-month-old Male JRT, Chip, we've had him since he was 9 weeks old. First, thanks for all the advice it carried us through crate training, house training, and puppy aggression! Now we're at the fussy eater stage - your advice there has also worked but now we have related problems. We did as you suggested, 15 mins then pick up the food. After a day or two he was eating fine. This worked for a few days / a week but then he wasn't eating again - but we kept to the feeding rules. This has gone on over a month.

Now the problem is, when we're picking up his bowl after 15 mins, he eats EVERYTHING he sees outside of his bowl. He doesn't seem to like the dog food but will eat everything he encounters outside. We have a large backyard - a huge fenced area with lots of open space and full of trees and 'stuff'. I can't possible pick it all up. He eats pinecones, sticks, leaves, roots.... When we're out for a walk he eats trash and if he sees some dog feces before I do it he chomps that down.
When he is eating 2X a day a home he doesn't eat much outside but when he's being a fussy eater and I pick up the food after 15 mins then the 'outside junk food snacking' goes up.
We have tried different dog foods, water, etc to keep him eating at home but after a couple days the 'picky-ness' comes back. Chip is driving me crazy on this one.

Thanks for all your help...