Extremely Active Puppy

I am new to this forum but have been reading through your posts and have already found some great information.
 
I have recently adopted a puppy from the local SPCA.  We love Scout very much and he is a sweet, sweet dog.  But...he is VERY Active!  He has spent two weeks with a professional trainer and he is wonderful while on his leash (with a pinch collar).  However, as soon as he is off the leash he is a tornado. 
 
According to our trainer, he appears to be a Jack Russell mix, but about twice the standard size of a JR!  We walk, we play fetch, we chase the kids on their bikes.  I just can't seem to exhaust him. 
 
Any thoughts on calming him a bit while still allowing him to be off the leash - at least while in the house?
 
Thanks for any suggestions.
Jenn