(I haven't read the replied yet, just responding to the original)
There are a number of different configurations for hose-routing, and ways of securing your regulators.
The absolute FIRST thing you must determine is
primary or secondary donate.
- With primary donate, you always know where the regulator is, and can assist the diver in an emergency faster. I believe this is the main reason primary-donate is taught.
- With secondary donate, your can secure your primary in ways it's nearly impossible to lose. You can also stow your excess hose using bungee or other means. If the reg is kicked out of your mouth, it's just right under your chin.
Once you determine primary or secondary donate, your
donate-regulator ideally is...
- ...breakaway. When your buddy is OOA, there's no time to waste. Your regulator should come free with a tug. Your buddy may even yank the regulator, causing additional trouble, if it's not breakaway. There are a number of ways of doing this, from breakaway bolt-snaps, to commercial or DIY necklaces.
- ...consistently findable. For your own benefit, both of your regulators should be retained in a way you always know where both are.
- ...brightly colored. Your buddy will more likely (but not always) reach for whichever one is brightly colored. I wrap my donate-hose in a bright neon color.
- ...long enough. That is long enough for your buddy to use, while you use your other regulator, and swim to the surface.
- ..discussed with your dive-buddy. Make sure your dive-buddy knows which regulator is your donate-regulator before a dive.
As far as retainer options, there are many out there. Hose clips, magnets, necklaces, loops which go over the mouthpiece and more. Just search a site like ebay for "scuba regulator retainer." There are also DIY options as well, such as a breakaway made using a bolt-snap, zip-tie, and bolt-snap. A non-breakaway necklace option is just a piece of bungee under the zip-tie, with knots on both sides.
Personally, my primary is a non-breakaway bungee cord, which goes under the mouthpiece zip-tie. My secondary hose is covered in bright-neon-green wire-protector material. My secondary is also clipped to my right chest d-ring, using a breakaway bolt snap.
When I do side-mount, the setup is the same, though I am switching regulators (because I'm switching left/right tanks), technically it's not primary or secondary, but one regulator is NOT breakaway, and the other has a breakaway bolt-snap with a long-neon-hose, and always clipped to the right-chest-d-ring when not in use.