About a year ago we adopted a dog (Garth) from a local shelter. He's about 4 years old now, maltese-shihtzu-poodle-something cross (a big ball of white and fluffy). He appears to have been semi-trained before we got him - he's toilet-trained and picked up sit/stay very quickly, though we did initially have a few issues with him escaping.
Lately we've been having issues with him getting into the kitchen bin. Its a relatively large freestanding bin in the kitchen, and when we're out he likes to tip it over, destroy the bag and eat any scraps which may be left in there. This is especially frustrating as his favourite place to eat his treats is on the living room rug, meaning that when we get home we're greeted with rubbish strewn from one end of the house to the other.
One final thing that has been a real issue when training him is that he tends to pee when he knows he's been naughty... meaning not only do we have to clean up the bin mess, but we get a nice trail of urine through the house as well.
What could be causing this behaviour? Short of catching him in the act, how do we punish him for this or otherwise discourage the behaviour?
Any help very much appreciated!