One thing that I would say is don't do it in the afternoon!!

We did and it was so incredibly hot. The horses were all sweating and "slippery", so staying on them wasn't easy. They had a track through the woods that we followed and the horses just plodded along this. Half-way round the guide made them break into a trot, which nearly killed me!!

If you are competent riders (we weren't!) ask them what they can do for you instead of what we experienced, because those who could ride on our "trip" didn't rate it much at all.