When Hearth and Home was released a lot of people were sad to see they could no longer train their skills by mindlessly punching rocks. I accidentally stumbled upon a neat new way of doing it and I felt like I have to share. These are just the very basic mechanics of how it works, which can definitely be optimized to be about as braindead as rock smacking was.
First thing you have to do is aquire at least 2 Lox. Build a big ol pen for them and start breeding by littering food all over the pen. Once there are a lot of Lox in the pen and a lot of food spread across the ground you can enable friendly fire and start whacking your Lox til they're about dead, when that happens move on to another lox. They'll heal from the food on the ground, so as long as you have a decent sized barley farm the Lox will have infinite HP. That's why it's also important to have a good amount of Lox in the pen. If you have something like 5 they might not heal in time.
I hope this helps!