I'm currently using Pro Choice SMB II boots and although I'm sure the protection aspect is great, I'm not impressed with their usability in sand and water. The arena at my barn has deep sand for reining, and the trails have a lot of water. Sand gets trapped inside of them and although it hasn't rubbed my horses, it can't be very comfortable for them. They soak up a LOT of water and become extremely heavy.
The SMB III boots and the VenTech Elite boots claim to keep dirt and sand out better, but what about water? Should I be looking at cross country boots?