Adding fresh manure to arenas usually results in a slick footing that takes a long time to dry. Manure is unsanitary and breeds flies. Horse manure that has been thoroughly composted into humus might be OK but commercial compost often contains heavy metals which can be a health hazard to horses and humans. Besides potential harm to the soils and groundwaters, spreading old tractor or car oil on an arena is very messy for horse, tack, and rider and can cause respiratory problems. SALT is used to prevent footing from freezing.
Salt lowers the freezing temperature of water by a few degrees.
However, since it is caustic, it causes problems with hooves, metal, leather and lungs. There are other products available today that do not have these drawbacks. Microbes produce binding fluids which hold footing particles together and prevent them from drying out. The addition of natural or plastic fibers to existing soil can both aerate the soil and bind it as well. Their success in arenas vary.