Have you put anything particularly interesting in your garbage recently? My dogs don't get into the garbage, but if I throw away a tuna can, or something really yummy smelling, they sometimes do. Perhaps they're just bored? Often dogs become destructive if they're bored or aren't getting enough exercise. I wouldn't want to put the garbage can on the counter, either, but maybe you could shut it away in a bathroom or something, at least while you're gone.