In timed events, leg collision can usually be more traumatic than in events like trail and western pleasure.
I use these sesamoid splint boots on this splint boots
page and I know some barrel racers who use the combo boots that are available there. They are pretty cool hind splint and skid boot combinations.
The prot-tec bell boots from equibrand are really good overreach boots. If you're barrel racing, you should defenitely get some.