What is the best arena footing for reining and speed events? Can you use wood mulch type for these disciplines?

Many different types of arena footing materials are available depending on your price range and desired characteristics. One of the most affordable materials is stone dust, but it can be difficult to maintain as it is highly compactable. The most common arena material is sand, as it is relatively inexpensive and fairly easy to maintain. Many materials, such as lofting agents, soil, or clay, can be added to the sand to increase active recovery, retain moisture, and enhance cushion and spring. Some of the lofting agents used include various fabric/fiber, wood, rubber, and plastic products. Depending on your budget, there is also the option of polymer or wax-coated sand. This material does not pack, so it requires very little maintenance and no watering. It is also dust free but quite expensive. This link might help you find which arena footing is right for your situation.
You have to consider several things before using wood mulch as ground fill in your arena:
1. Do you know the source of the tree/bark? If it (or any of it) originates from black walnut or other trees known to be toxic to horses, you definitely do not want to use it, or you will create more problems than you have solved.
2. What is the size of the shredded material? If “rough shred” material, sometimes referred to as hog fuel, is used in footing areas, it can end up freezing in an “up” position after a hard freeze and cause abscess, bruising, and lameness troubles.
3. Also, depending upon how the footing is processed or how deep it is, sometimes bark/mulch can get slippery if it gets too wet and/or frozen.
Aside from that, with any organic material, there will be decomposition, so its effectiveness of fill may be time dependent.