here are some things you can do .

1. create variables using a random number.....random(2000);
2. search strings looking for a certain combination of characters such as .jpg....png etc
don't allow the script to continue to execute unless the proper characters are found

3. encrypt all data outside flash using php or other encryption software before pulling it into flash.
4. create a secure directroy for all your php pages...then use include or include once statments to pull your php into any html pages you are using.
5. secure the directories that contain you .swf and use html not java in your html pages to pull in the .swf

Use loadvars and php session variables to store data or server side actionscript using flash media server

bullet proof no .............better than nothing yes!