From a post to Baen's Bar BuShips dated January 20, 2002:

Warp point denial II

If the defense [using a railgun to fire a stream of iron slugs into the warp point - Ed] were allowed -- which it isn't -- there'd be no need to use a rail gun; just dropping in the garbage Arnold suggested in his original post would do the job. Unfortunately, you can dump stuff through a warp home till the cows come home and it will have absolutely no effect on ships (or objects) transiting in the opposite direction. Which means that any defense based on obstructing a warp point, or shoving stuff through it, is going to be ineffectual. In short, this won't work.