Referring To Array And Adding / Removing One Preset Item

I'm trying to automatically add and remove one criterion from an autofilter without disturbing the previous existing criteria The autofilter code sounds like this:

Code:
ActiveSheet.Range("$A$1:$L$47").AutoFilter Field:=6, Criteria1:=Array( _
"Clay", "Grass"), Operator:=xlFilterValues

How would I go about referring to this array and adding another item called "Hard" to any pre-existing elements in this array?

I plan on attaching this code to a button and use it as a filter, so when the button is pressed, the item will be added to the list of criteria, and if it is "un-pressed" the item will be removed.