I've made fence before you need either fondant or gumpaste. You can mix them together too so that it dries quicker.. 100% Gumpaste always dries the fastest though.. Mix in your color like you normally would and roll out your fondant/gumpaste kinda thick. Use a knife or pizza cutter to cut strips of the fondant/gumpaste. Cut the strips to the desired size and then while it's still soft use the tip of your knife, a fondant tool or an xacto (used only for fondant/gumpaste) to make lines in the strips of fondant/gumpaste. There's no science to putting the lines it, just make some lines, I also add some curvy lines to some of the strips. If I am making it look like wood I will mix some brown coloring and vodka or vanilla together to make paint and I paint over the grain that I made for the wood pieces. The coloring sinks into the cracks and gives it some depth..
I hope it helped you can PM me if you have any more questions..
Oh make sure it's completely dry before adding it to the cake so that it doesn't bend.. If you weren't looking for directions using fondant/gumpaste, sorry I typed so much..lol
If you are making the fence with BC im sure this video will help
if you are in a hurry and need something fast and easy, you can use pretzels to make a fence or rail around your cake. looks great, fast, easy, don't have to wait for it to dry. mix the round and stick pretzels to make your fence design. very interesting and easy.
Goodness, i wasnt expecting such a great reply, iv been on other forums before and no-one seems to reply!!
Im having a mini stroke today, as i need to do this for Saturday, so il go through all your great ideas and do one of them.
Thank you again........ 
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