If I didn't mention it before, there is one more addendum I'd like to make:
If you want many shinies, such as in the range of over 100 from a successful chain, don't be drawn to every successful shiny patch you see. If you enter a patch on an unsafe tile (that is, a tile that is not surrounded on all sides and corners by other grass tiles), that happens to be a shiny patch, there is a chance you chain will end. Probable or improbable as it may be, it can happen. If you find a place in the grass you can stand, where you protect as many 3s from contact with the outer edge, even if you sacrifice 4s to do so, so long as any shinies show up in 1s, 2s, or 3s, you can enter them with confidence your chain will not break. If there are 4s not surrounded, remember, you run the risk of chain-break, despite the obvious reward. Likewise, caution is your best friend. With enough time, you can spend as long as you want waiting for 2-2/4-2 patterns to appear. At the cost of more potential shinies later, you can use your Repels to instead cautiously build a chain.
In my chaining experiences, in particular, with my shiny Torkoal chains (which surpassed 160 in length) I've passed up dozens of unsafe 4s, but I knew that with that somewhat small sacrifice of one shiny, I kept the path safe for dozens more. Enter only protected shiny squares, and the only risks you have for not encountering more shinies is running out of PP for Spore, False Swipe, Seismic Toss, Night Shade, etc., which is easily remedied by mass-growing Leppa Berries in preparation, status or running out of health, fixed by Pokemon who can heal themselves and require PP recharge to do so, or by stockpiling on healing items such as Hyper Potions, Full Heals, and Revives, easily bought by Amulet Coin/Vs. Seeker money-reaping south of Hearthome, the player's own clumsiness at walking into patches they didn't see, weren't paying attention to, etc., which is a point I can't help, and my personal favorite... running out of space in your PC Boxes, which can be remedied by depositing as many of your Pokemon as you can into My Pokemon Ranch; assuming you keep them in ordered blocks of 30, deposit and withdrawl are relatively simple.