are you sure you want to give the dog the boot? do you want to try training him - especially if he is so young.
the thing with 'one chance' is that he doesnt have a way to figure out not to do that again. we have a heeler mix. she is a pain, stubborn, grumpy and has a bad attitude. and she grabbed one of my hens. once. that was it. and yes it was A Very Sad Day To Be A Dog. but she never has done it again.
my two shepherds - about 8 months... that seems to be some turning point then again at 2 years - got 2 of my hens.. really they were just playing and it wasnt predatory. but i worked with them and now they really are a huge help.
give Mr. Hen Grabber a job to do with the hens like, sit over there while you get the feed. it can be anything just so he is involved. have him go around the hen house or do a perimeter of the yard . tie his leash to your belt and have him come with you every time you go out and correct any interest in the hens other than rounding them up or finding a lost one.
my dogs are invaluable to my work on the farm. they do everything from help me find lost chickens, warn me about hawks, and keep the geese in check.
most working dogs - like heelers really just need a job to keep out of trouble. as we say here, a tired dog is a quiet dog and you should exhaust him every single day with work work work.
just some thoughts - good luck!