I love oak trees (our national tree), but not so much the acorns - in France they root really easily and very quickly put down deep roots, becoming difficult to remove without digging really deeply, which of course disturbs whatever other plants are in the area. So if yours just sit on the surface, you must be doing something right!
Hadn't thought about it before, but we don't have the same problem in England, where we have more and much bigger oaks.
