Don't dig or walk on the soil when wet.

Use the right tool for the job, such as a pry bar to remove large rocks.

What if the rock was 12 inches down and you did not realize it ;-)

Maybe I need one of those similar to those guys that walk the beaches and look for metal, instead mine will be for rocks.

That wasn't intended as a criticism, a1an, just an example that was triggered by your rock experience. There have been shovels broken in my household when someone I won't name tried to use a shovel to pry a rock out.

I could have just as easily said to use a saw rather than loppers when a branch is larger than 2".

A corollary to the right equipment would be to use the right safety measures such as wear shoes when using a shovel since if your foot slides off you can slice tendons and use hearing protection with power tools.