Labs are relentless when they are hunting and Boxers are hard headed. LMAO you go tthe best of both those worlds I see. Training, training and still moretraining is all I can tell you to break that habbit. How old is the dog? When you see the geese outthere get him out there on a leash and let him watch the geese and everytime he makes the slightest move tell him NO! Stay! Don't touch! I use Don't touch alot with mine. If you can get the dog in a sit/stay and keep the dog there no matter what eventually the dog wil get the idea. Chances are the dog wil not catch the geese so every now and again after he starts sitting calmly with no indication of trying to move away after the geese let him go for a bit but keep the dog on a very long leash. If the dog goes toword the water with the intention of chasing the geese say NO! Don't Touch! and call the dog to you. If the dog refuses to come you have the dog on a long leash so pulling him in to you is easy. Then immediatly back into a sit stay position. Eventually the dog is going to understand that freedom is given so long as obedience is recieved. You will be surprised how fast the dog will learn. This desire to chase the geese is a natural desire for the breeds you have so be patient.

As for the long bouts of swimming we had a yellow lab once her name was Baby. We found her at a gas station nearly starved to death. Well we took her home and got her healthy and every day we would go to the river. (We lived right where the sawannee and the santa fe river met in Florida.) anyhow if we didn't take her she would run following the van all the way the 5 blocks to the river. She LOVED the water. And she would fetch a tree limb all day long. Just as long as it was in the water. She looked exausted but she wanted more. Just swim, swim, swim. One day the river had a bit of a strong current to it and it took the branch a ways down the river and she lost sight of it. We watched that branch and her for  a while until we couldn't see the branch anymore it was way down the river. This dog refused to leave the water without that branch. We tried throwing others in and it didn't matter she wanted THAT one. After an hour and a half straight we could see she was getting tired but still she would not come. She had been swimming all day for goodness sakes. My hubby had to go out and get her because she started to struggle. Long story short yes your dog can end up in trouble just as mine did. Dogs HAVE been known to drown this way.

And BTW Canadian Wild Geese are protected. And I have to disagree because Labs are very intelegent dogs.