The way to do that is to make a component of each type of picket. Then they each need a hidden attribute asigned to turn them on or off. Then make add a user defined variable to the outermost fence component. Set it as "Users can select from list". Then it will give you a list that you create. Add a name for each type of picket. Lets say there are 3 picket types. Put them in the list like this:
Plain - 0
Rounded - 1
Ornate - 2
So now the user will see the name and can select what type of picket they want, and the menu will return a 1,2 or 3 as its value.
So now you have 3 separate picket components and a menu option for people to choose what type of picket they want. Now you need to hide all components that are not selected. Do this in the hidden attribute. (I need to mention that we'll use "PicketType" as the user defined variable that creates the menu item that the user selects).
Picket 0 should look like this:
Hidden - if("PicketType"=0,0,1)
Picket 1 should look like this:
Hidden - if("PicketType"=1,0,1)
Picket 2 should look like this:
Hidden - if("PicketType"=2,0,1)
That will set each picket component to be visible if the user has selected it from the list. If it is not selected, then it will be invisible. This will be set to all copies of pickets too (I hope).
So give that a shot, let me know if it doesn't work like I think it should,
Chris