If you want a good fun day out horse riding I would recommend Xilihu in Shenzhen:
SNI Equestrian Centre (Xili Hu Ma Shu Zhong Xin)
Xili Lake Holiday Village (Xili Hu Du Jia Cun)
(0755) 2651-1743, 2651-3006
http://www.shenzhenparty.com/sports/
RMB250 for one hour, but you normally get close to 2 hours for no extra charge.
They have a huge place for riding, great scenery. The route i normally ride on goes through a lychee orhard, farm and reservoir. Takes an hour to reach the reservoir and an hour to get back to the stables. Really good fun.
Catch ferry to Shekou from Macau ferry terminal in Sheung Wan and take a cab there.