Now that you have determined where your trenches should be, it's time for the fun part, the real work, the hands-on stuff.
Whenever I think of digging trenches, I think of World War One. World War One was a classic struggle marking the peak of static defensive warfare. When I was a student in high school, I read "All Quiet On The Western Front" and saw Gary Cooper play Sergeant York. Ever since, I have been intrigued with the idea of digging.
As you can see, when I began digging the trench, it was a labor of love. I hoped to duplicate the World War One experience. I even bought two of those Nerf guns so my wife and I could have a safe, minor battle when we had dug to a sufficient depth. The only problem with this scheme was that digging a trench is much harder work than it looks at first glance. I thought I would only have to toss a few shovels full of dirt.
Had I utilized my wife and her degree in mathematics for anything more than menial labor, I might have calculated before-hand the volume and weight of dirt that I had to move. A trench ten feet long by two feet wide by four feet deep comes to eighty cubic feet. Figuring five FULL shovels per cubic foot, that is 400 shovels tossed over your shoulder. Figure in the amount of dirt that will fall back into the hole, the rocks to be dug around and the monotony factor. All of this adds up to one thing: a sore back at the end of a long day, and you still haven't got enough trench for even one wall of your addition or one decent pretend battle, for that matter.
I found my dreams of recreating World War One turned into a real war; only I was not fighting the Germans with Sergeant York at my side. Instead, I was fighting the trench itself: battling cave-ins due to unexpected precipitation, hammering on that underground gas pipe the gas company forgot to mark, and testing out some dynamite my senile grandfather told me would make the job a little easier.
Although, I finally won the trench war, it was not without struggle, disillusionment and a visit to the chiropractor. I admit, for all of my fondness for the shovel, the blisters growing on my hands gave rise to some animosity towards the tool in the rest of me. But, by God, it was all worth it. I can confidently say when I show visitors my addition that I dug the foundation myself, by hand. If they question my sanity, I simply stare them manfully in the eye and tell them, "Digging that foundation is an experience I would not trade for a trip to any field in Flanders."