With my dogs, I leave their food down all day, and fill it when it is empty until 5pm. I usually fill it about 3 times, it is a big dish. I go to bed at 10:30 so this gives them enough time to go to the bathroom a couple of times before bed and that way there are no accidents when I wake up and they are eagerly awaiting me to take them out.

I've sometimes thrown a handfull of their dry food onto the lawn so they have to hunt it out. I have recently been told to take up food after 20 mins by a trainer it was really hard at first the dogs would just nibble a bit and just assume that it would still be there later but now i think they get it, you eat when it first goes down or you go without til later.

Yes - I think that is probably the best way. Unfortunately, once the food has been removed, Oscar just eats whatever he can find - plants, pebbles, slugs, chair legs, carpet - you name it. So, I am still at a bit of a loss really.

I take Max's food up after about 20mins...

I think the eating other stuff isn't because he is hungry, but because he is curious. Max likes to taste everything with his mouth first (like carpet tiles )

Lula is the same. If she can get it into her mouth, it's in there . I'm constantly fishing obstruction sized items out of her mouth.