To keep Jarvis interested on walks (to try and stop him running off again!!) we invested in some training dummies. He goes absolutely mad for them, tail wagging like mad as he sniffs around in the grass trying to find them.
Took him to the river where he swims every day. Got there at the same time as some other dogwalkers that we've met on the circuit a few times.
Threw the dummy into the river (not attached to a cord or anything) and Jarvis jumped in, got it, then brought it back to drop at my feet. He repeated this about 4 times - I was so proud - he's not even 6 months old yet!!!
We then crossed the bridge and into the field opposite. Just as I threw the dummy into the grass, he was distracted by the arrival of another dog so didn't see where it landed. I wasn't sure so started looking for it...
...it turned up in his mouth after about 5 minutes... good little boy!!!