There is really no protection against decompilation. I have the current version of Refox and have used the highest level; but this can be (and has been) decompiled. I received an email from some individual on the UT demonstrating his capability to decompile any level of Refox (he sent decompiled examples). His email was set to not give his identity -- he wants to remain anonomous. He claims he can also decompile any format. I asked the purpose of his utility -- he indicated that it was for his own use.

So You can try to make it hard to decompile, but there is not really a way.