We have a Buckeye tree in the back yard and he's been eating the seeds. We've just found out about it (we mvoed in recently) and apparently they can be poisonous, causing tummy upsets (not seen) and hyper-excitability (seen a lot of that!), so we're keeping him on a lead in the back yard and he's really really mellow with bouts of normal puppy exuberance since, which explains why he was going a bit insane. He had his 12 week jabs the other day and the vet said to keep him in the garden for another 4 weeks, but at puppy school last night the trainer said it's really important for him to get out and about and socialise, as that is more important, so I took him for a little walk this morning and he seems to have burned off some of his energy.