The object is to promote the good of society as a whole. That means protecting some from harm and protecting others from lawsuits. The trend is that the"others" are commercial establishments. Because business is good for society. Commerce is good for society.
Many non-commercial horse owners think they are covered when they may not be. Now go read your state's equine liability statute and see if it covers you? Some exclude racing establishments. Some exclude stallions.
Some states have strict liability which means if it happened you are at fault--no reasons or excuses allowed. Is your state like that?
And the nagging thing about spectators still bugs me. Last year I offered to help draft a plan to limit liability for a local horse related event. The best idea I could come up with was a ticket. On the back of the ticket is the assumption of the risk stuff. That's pretty common in concerts, baseball and other places people gather and may get hurt. If I were organizing any event where horses often run loose through the crowd--steeplechase, point to point, eventing, barrel racing (you-tube it). . .I would take the time to set up a gate and issue tickets.
Its is important to understand and customize each situation and I just can't say enough how much I worry about releases being passed around the internet from person to person and state to state. I actually think most of the time the lawyer drafting the release should come out and do a liability inspection because lets face it, we see liability all over!
If you rally cannot afford a lawyer then do your homework. Read the statutes. Read some recent cases. Look at many examples. Think it through. Lawyers win and lose cases based on where a comma is placed or just one word. Its that nit-picky.
If you knew or should have known is powerful stuff. You can't deliberately not know because you should have known. So how do you know what you should have known? What standards are applied?
Some of it is just custom. In a H/J barn you should have known helmets were mandatory. In a western barn they are not used at all. An up down lesson has different risks that something called a suicide race. Its all relative to what is customary and normal for your area and your sport. Do you teach Western and English lessons? How do you know when helmets are a must and when they are a maybe?
Look around. Do what the majority does. Do more is you want, but never be in the minority.