Trust me its not as easy as it sounds. I had alot of trouble with riding outside of a pen. I always felt that if the horse was loping it would suddenly get out of control, and try to run home, leaving me behind. Since I've been training horses and had to work on that I really changed my mind. I learned that the horse knows all you're cues and being outside the pen is hard for them and if you're nervous you're just making it even harder. If I feel like my horse is getting out of control I usually just make a small circle and try again. I have learned that if you keep calm and learn that timing is key then you can do anything, and get through those bumps in the road.
I've found this to be very true (and good advice) for less experienced riders.
We always want (and expect) our horse to trust us, and we must trust our horse, too. Keep in mind that the horse is a social creature and it has accepted
having a rider, not been forced to have one. It is a true, willing
, partnership between horse and rider.
As mentioned, if you think things are getting out of control, do a circle or stop, have your horse take a couple steps back...take a deep breath, give your horse a rub on the neck, and continue when you're ready.
As with working young horses, time in the saddle is key. The more you ride, the more relaxed you will be.
Relax, enjoy, have fun, and good luck, and don't worry about anyone else.