I think my trainer uses one of those gels in the Cover-All arena, and it works pretty well when used with minimal water I believe. I will ask her what the product is during my lesson on Tuesday and get back to you : ).

You can have some of our rain, here in NE Ohio we've been getting nothing but that for the past couple days! Good luck finding a solution : ). Riding in the dust = no fun.

We use waste vegetable oil on our sand surface.   my arena is 100x200 and i use approx 150 gallons,  Works excellent on sand, not sure how it work on your mix, but it can be a free solution! and safe for the enviroment.

We used a product called MAG in our Indoor Arena, but apparently it works well outdoors as well. It is basically Magnesium Chloride, in pellet or flake form. It is used for de-icing in Winter here in Canada, but it is the most wonderful and effective product for controlling dust.

Go to http://www.meltsnow.com/products-mag-dust-control.htm for more information, and to also locate a dealer near to you.

On dealing with rocks, we just pick them! We have regular rock picking parties where everone comes out and gives a hand with the rock picking after we have harrowed. In a while, you should have no more rocks left. 

 You should look at this product. A few years ago when I had my horses at home, I looked at getting it for my outdoor arena and the price was around $1000.00, but I thought it'd be well worth it.

 http://www.watersorb.com

When we had the natural arena, we just removed the rocks by hand, which is a pretty thankless job. 

For moisture w/o having to go the chemical route, and slightly less expensive, my friend has a lovely natural sand arena.  While she does have plenty of water w/her sprinklers, the ring often needs more spring (lots of horses go in this ring), so she has a large dump truck of green wood shavings come and then she mixes/drags them together.  The spring in the arena is very nice and the bonus side effect is that she does not need to water nearly as much since the wood shavings hold moisture.

 We are getting ready to finish the final layer of my arena since the base has finally set.  Although still debating, we are going with 1/2 stone dust + 1/2 sand with a mix of filler for 2 inches of footing.  I'm not sure which route I would go if the parameters that concerned me was strictly dust.  Depending on the amount, the wood shavings eventually will break down (of course) and then they too will get dusty (which is when you add more).  The rubber is fantastic, great to ride on, but is expensive. I don't know how much it would cut down on your dust either, I would think if you put enough in it it would.  The one I've ridden in was just always perfectly groomed (including between horses).  Do you know if the rubber would reflect heat?

 At the stable I ride at they have treated the indoor with a product from Petro-Canada call Dust Suppressant Fluid 65  ( http://lubricants.petro-canada.ca/resource/download.aspx?type=TechData&iproduct=714&language=en ).

 It is odorless and non-toxic and there is not a speck of dust in the arena.  It also doesn't seem to stick to everything like other oils