What are you really trying to do? Who are you trying to prevent from accessing this function? As you can see from other posts, this is a security issue. Security problems have solutions, but we need to identify the problem before we can find the solution. Identifying the problem requires us to
- identify who/what needs to be protected ("What assets are you trying to protect?"), and to
- identify from whom/what it needs to be protected ("What are the risks to the assets?").
Could you elaborate on these topics. We can't develop you devise a means of protection without clear information on them. What you told us to be protected sounds too specific, and we have no information on that from which it should be protected.