Symmetric encryption. For mutable data, we use a fast XOR encryption: the data space used for the content is doubled. One is for the data encrypted and the other is for the random key. This approach guarantees such search tools would fail. Only advanced ones would work, and I don't know any capable of exploring it. Instead of searching for only one field, it needs to search 2 and XOR it, so the search complexity would be O(N^2), a way worse search, but still viable.