We need to start a document 10x10 and we are going to trace an X such as the one you see in the picture. You can copy it if you don't want to do it.

To do that you need to use the magnifying glass of course and make it as big as you can. When you are done, click on Edit-Define Pattern and when the pop up window appears, give it a name.

Next, lets find a picture where it is appropriate to put a fence on.

With the Rectangular Marquee Tool, draw a rectangle in your picture and keep in mind how high you want it since this is going to be where we are going to put the fence.

Choose the bucket tool and then change it to fill and from the drop down menu select the pattern we just created.

Create a new layer Layer-New-Layer and fill the rectangle you just created.

Change the layer mode to multiply and click Select-Deselect.

And here is your fence!

you can add things if you want.