And another tip - feed them at night time, when they would normally be active finding food (in the wild). Once a day. That way, they either eat or they're very hungry the next day when the food window opens again.

That's one of the other benefits of the vet dry food - they eat a smaller quantity (because there's less filler) and if they don't eat it one day it's still "fresh" the next, so there's no wastage (unless your naughty little dog sneaks in and woofs it down).