Hi there! I just adopted a BC mix about the same age - also a "boomerang" dog (multiple rehomes) from apparent boundless energy...
Week #1 was insane. I thought I was going to have to call in help to work with the pup, but in the end it seems like it was mainly "new home" energy for the pup (and me ). Marking/peeing is still occassionally happening, but for the most part Week #2 we've both settled into a schedule and I'm getting my own work done. Week #3 looks like I can leave him alone for extended periods now with my other housemates.
You can train in some calmness into your pup!! Check out advice, like from this book "Chill out Fido!": http://www.dogwise.com/ItemDetails.cfm?ID=DTB1061
Basically throwing a towel/blanket down in a room and rewarding the pup anytime he relaxes on it (chewing/lying/playing, so long as it's contained to the blanket). This worked really well to teach my 5 month old BC pup that being chill was cool
I also use crate training during the day as well, just in times of the day where I know I need to work and he needs to learn to settle/alone time. Frozen ice cubes with dog chow inside or a little chicken broth also offer some entertainment.
GOODLUCK! & Let me know if you find any tricks that work for your pup, I'd love to know!
