First, why?

Second: is your app a critical one?

Is the information the important (ie: credit cards or customer or medical info) or the app itself (mmm... a app for national security?)

Take in account that get real information from a decompiled app is hard...

Also, a decompiler like refox have a re-redecompiler....

Anyway, is sure that you have a good reason, and in this cases we spend much time & effort, so i suggets this article for service-based protection against crakers, hackers and pirating (no relating to a "tech" tool ;).... enough for normal apps, that its, things that put in the dust a hard-cracker because brute-force used in decompiling&cracking is replaced (or, in your case, if a tech tool is used for protection, put it more strong) with things that only you can provide...

http://www.hower.org/Kudzu/Articles/Piracy/index.html