hrm, send a lf with it ?
or a button that turnedit off for a specied amount of time?

The DF matter is good as it is.
I don't think its fair to change this since people raid for profit and this way profit seems to decline.

Or just to make things easier just at lvl 6 missile silo add a Debris Field Mine to the defensive options on that planet that way if you have a huge field only some will be taken. Also make them take out 5 or 10 recycler's at a time. Just an idea.