Wipeouts might be tricky sometimes, especially when nested within crossreferences. I always check the Object Type List within the Quick Select to find out about wipeouts. Xclipping might be tricky too, so I opt for the following method.
 
You can create a polyline or pick points on existing geometry to create a solid hatch. The trick is to:

1. Bring the solid hatch to the front to hide what you need to be hidden.
2. Pre-create a layer with true color 255, 255,255 and move the hatch (and optionally its boundary) to the selected layer.

Since the true color is white, you won’t be wasting ink and everything behind will automatically disappear. Of course, if you need to reveal and hide again and again, you can freeze/thaw the layer.

Notes from Cadalyst tip review R.K. McSwain: If you have tried the ideas in Tip #4351 and are still having problems with wipeouts, take a look at this alternative that uses a solid hatch entity.