Alright I guess I'll start this off with a few things I found helped with DexNav searching in non-grassy areas:
I was in the Unown Mirage Cave and was having trouble maintaining my shiny chains, as they are extremely hard to keep in Water and Caves, because the Pokemon moves AND if it spawns on a spot that you are on (recently found if it spawns too close as well), it simply runs away.
However, I had a couple of ideas based on testing I had done in the past, and just tested them in ORAS to help with Dexnav Shiny Chaining in Caves and Water specifically to VERY GREAT effect. (It essentially cuts down on item usage, and creates a sort of safe zone for chaining). This is mainly for people who use Dexnav in Caves and in Water, as it is much harder to chain in these places than in grass, though it can be used for grass too. So just in case you all want to try it out, I thought I'd share.
While chaining for Shiny Unown I found that using the search feature takes a very long time, as caves do not have a higher encounter rate when using Dexnav (based on my experiences). Because of this I thought "I wonder if the D-Pad trick works in this game, and if it works for the Dexnav?" In case you do not know what it is, the D-Pad trick is utilized to cause an encounter by tricking the game into thinking you are walking, without actually moving any steps. To pull it off, lightly tap in any direction BESIDES the one you are facing (but go in a cyclical pattern as it's easier to control) and your character will turn in that direction without moving. I learned that by doing this, one can cause a Dexnav Pokemon to usually appear faster than using the search function. However, you must have a Repel of some kind active, as doing this without a Repel can also cause a normal encounter to happen (Repel steps are not used up doing this trick, as the counter only goes down when you actually move to a different tile). By doing this in areas with only one or two Pokemon, you can greatly increase the amount of Hidden Pokemon encounters without wasting steps (and in the case of the Unown cave, there are ONLY Unown, so I always get an Unown encounter ). And since the Pokemon is being found via Dexnav (any kind of shaking spot or Pokemon hidden in the ground, water, etc.) the chain continues.
Edit: I tested the D-pad trick with the Search Function, to see if the "trick" effect carries over to the search function, and it seems like it does. I tested it standing on one tile (changing direction clockwise, and after abut 6 times of it saying the Pokemon couldn't be found, the search feature picked up a Unown).
The Second thing I tested and was elated to see return is the TM PP trick. The best way to utilize this trick is in conjunction with the D-Pad trick and Synchronize when chaining. The way this trick works is simple. Teach any TM move to a Pokemon of your choice, as long as it can also learn a different TM not already on its Moveset (I'll use my Synchronize Espeon as an example). It knows Hidden Power (Dark, Specifically for Unown) Psychic, Dazzling Gleam and Shadow Ball. Step 1) I continually use Hidden Power until it has 1 PP left (have not tested this yet with 0 PP) Step 2) After the battle, I teach Protect over Hidden Power which only has 1 PP left. Step 3) after I teach Protect, I RE-TEACH Hidden Power OVER Protect. By doing this, all of Hidden Power's PP is restored, without the need of any items or O-Powers. This can be done indefinitely with any TM moves as long as both moves are TMs (meaning you can continually alternate between them). This way, you can keep your Synchronize Pokemon as your lead and never be worried about PP.
I have just started using these tricks, and so far I have increased my short chains of 1-4 because of bad spawn locations to 5-15+ where I can comfortably continue chaining even with the speed up that Hidden Cave and Hidden Water Pokemon get after the 4th/5th Pokemon in a chain. Hope this helps all of you out too and happy hunting!
Note: Chaining does not seem to increase the chance of a shiny. Rather, it seems to increase the chance of higher levels, IV's Rarer abilities/Hold Items/Moves etc. It does not seem to increase the Shiny Rate continually, so it's been speculated that it has a fixed amount.