There's been talk of special shiny encounter codes which involves performing certain actions whilst playing, as well as inputting codes. From what I've heard in this forum, you're more likely to glitch your game if you have to follow certain actions, or if the code you have to input is a long one. My advice is, don't try it! I glitch enough on the regular codes, without doing something complicated.
If you want to get a regular deoxys, though, you don't have to wade through putting in encounter codes, however. Look for magic door codes: the magic door itself is twelve lines of code, with an additional two lines of code for each place. I've found that the place codes are identical for LG and FR, so once you have the codes for one game, you simply repeat them for the other. I got my codes from Codejunkies.com: there are other sites that do AR codes.
Word of warning: if you use the magic doors, save your game, then switch off and remove the AR. If you don't, the game glitches, and you don't get to either the birds or Deoxys.