A 18 week old puppy

:lol:  hehehehe....wait until he goes thru puberty!!!  :crazyeye:
To teach him to stay in the yard and to come when called, I use a 30 foot leash. It will take 2 people, one to stay with the dog, and you to go 30 feet away and call him. The person with Kota should have him in a "sit" and "stay". Kota should wait to be called to you. When he "comes" give him tons of praise. To keep him in the yard, have him on the leash, and every time he steps out of bounds, step on the leash and use a command, "no" "stop" "inside" whatever you choose to keep him in your yard. It helps if distractions go by, like the kid on the bike, a ball, a bird, another dog, etc. It's worked for my two so far. I have no fence and my dog enjoys the backyard and doesn't step out of bounds.
It is very common for them to go through these changes, sometimes they aren't good changes either! I'm telling you...be prepared for puberty! You will have a little monster on your hands!  
As far as the must have treats, as long as Kota doesn't have any weight issues, mine go beserk over cheese cubes or as gross as it is, Liverwurst! I use the liverwurst to hide meds in, and found out dogs go crazy for the stuff! A little dab will do ya! Good Luck with the training....in the end it is so, so worth it!  

Oh I'm sorry, I had to laugh.....Even my lovable old man Samson does that still at the ripe old age of 10....Boxers are late bloomers, so like Tootsie said, about the time they hit the "teens" people get frustrated and give up, hence so many in the shelters....It does take patience, oh boy does it....There have been times I would cheerfully pull my hair out to refrain from doing what I really would like to do......It very much is a battle of wills, esp as you are both males..That's one of the issues I am dealing with with Angel..We are both strong willed, hard headed...well you get the picture.....

The lead is an excellent idea, by the way..Great way to work with him to learn to "come" when you call...Use his name over and over again...As for treats, mine have loved everything I have ever gotten, but I think I also used those Authority treats in class and Samson loved them..Trial and error there...I actually bake my own cookies now for mine, so no more store bought treats...

Take a deep breath, repeat to your self, this is just a phase, it will pass, and if you drink, have a nice tall cold one...Lol....Can't wait to meet you both at the next meetup..He sounds like a character