We have a medium-sized mutt who appears to be partly herding dog of some sort; she's 6 and has tons of energy but she's not getting as much exercise these days since our son arrived.
She seems like a good candidate, but is there anything special I need to worry about? Aside from keeping her hydrated and not runnning her over. I was thinking of Sals and SME; I dunno if she'd keep up on sustained fast sections like at Trex, but not sure.