How to prevent Java reflection to access a custom Java package in a custom Android?

Let us say I have a custom Android 4.3 with a custom java package xyz.java.

My questions are:

1. How to use Java security manager to prevent apps from using reflectoin to enumerate Java methods in my custom Java package xyz.java?
2. Where in Android source code should I put the Java security manager code (suggested in 1) to prevent apps from enumerating methods in my custom package xzy.java?