To pin your dock to the bottom, just type this into the Terminal:

defaults write com.apple.dock pinning -string end

Or if you’d rather pin the dock to the top or back to the center, simply replace the last word of that line (end) with either start or middle respectively.

After typing this, you’ll need to reboot your Dock. Do this by restarting your computer, force quitting the Dock from Activity Montior, or typing this into the terminal:

killall Dock

If fiddling in the Terminal freaks you out, there is the more-than-capable app, Cocktail, that let’s you adjust all sorts of settings for your Mac, not just where to pin the Dock.

Done and done.