Hello! I could really do with some good advice here...
We are dog-sitting a friend's 8-month old Cairn Terrier (male, neutered). He lives with his owner (single adult) a relatively calm existence, spending the evening snoozing on the sofa, listening to Radio 3. In his own environment he is (for his age) quite well behaved.
In our house (and this is his second stay) he is no end of trouble and very destructive: chasing the children, chewing things (anything he finds on the floor), barking at all manner of sounds (kettle boiling, wind in trees etc), digging bloody great holes in the garden, stealing food from tables/counters etc etc. On his first stay he wee-d all over the house but this time he is, thankfully, housetrained.
We also have a dog - a 7 year old lab/springer cross and they get along famously. They spend three days a week in the office together so they are very familiar, as indeed, I am, to him. When our dog has had enough of his mischief, he gives him a Big Top Dog woof and they both settle down together.
I'm aware that the boundaries are different here from what he is used to - he is usually still walked on a lead as his recall is not good - whereas here he has the run of a big garden. He is not used to children - but he loves them! It's all a bit bonkers here, perhaps, and very unsettling for him.
Does any one have any words of wisdom before he completely trashes our house and garden?
I don't want to confine him to the kitchen but we need to do something to help him settle. We've trained our own dogs before but and instant training tips would be much appreciated! 
Sorry it's a bit long. Thanks for reading.