I'm sure there is no perfect solution, but I figured I would at least try.
I have had a farm for about 4 years now. . .teaching small children to ride. Every year we rented an indoor for a sunday and would trailer 3 of my ponies there. Each year getting bigger and bigger with students. Last year we started to rent the indoor and 2 weeks into it, we just thought it was ridiculous considering what a nice winter we had last year. It spoiled us staying home and teaching like we normally do. This year after a lot of thought we decided it would just be too much. . .too much for the ponies, too much for us, etc.
So now the question is, that we got snow at Christmas. .. now almost 2 weeks later the snow is gone, but from it melting has left ice . It is warm enough to ride, but by the time night falls it is all ice and too dangerous to ride on. . .
So am I just going to have to cut my loses and teach when it is warm enough and see them consistently in the spring again? Or is there a way to get rid of that ice until the next snow fall anyway. . .Currently trying pet safe rock salt. . .we will see how that goes.
I would not ride my horse on ice with ashes or sand added as 'traction'. One slip and you can have a horse do a split and get injured and not come back for many months. I am very cautious with my horse and ice - I shoe in borium and snow bubble pads all around for the winter snow and ice, but I only ride in deep enough show that there is no risk of slipping on ice. I also don't ride on frozen ground much - its very hard on their legs. Not much options except and indoor. If you want to keep a horse in work over the winter, I guess trips to an indoor are worth their weight in gold. I also do alot of longeing just to keep the muscling up, if possible, even if the footing isn't really good enough for riding. I don't know what to put down for melting. In an arena, I wouldn't worry about it having to be pet safe as much as I would be concerned if the salt was drying out the hoofs, but they could be rinsed afterwards I suppose
Trainer's website - photos of my horse Airborne under About and Francesca Edwards also in media page 1
We are in the same general area as you OP. My trainer just put salt down and dragged the ring multiple times. With the snow we got last sat we were riding in the ring by Monday with the footing being great. Now I don't know what her footing is but it is amazing!! We really don't loose too many days of riding when the weather is bad.
Probably will not try things for traction, only because the kids are so little and wouldnt want the horse to take a bad step or scare the child. . .just not worth it. I will keep my horses longed in the areas where there is no ice for now. . .and try some of the other suggestions with the salt down and dragging the ice and looking into the magnesium chloride.
Maybe next year will go back to renting an indoor, but I went from having 4 students to 20, to 60 very quickly. . .(just me and a small backyard type farm), It's impossible to teach 60 horse crazy kids without me going crazy and souring my ponies in one weekend.