I don't think there's any one way to tell if this will be their "thing". There are things that Tara does that show me that she enjoys the mental and physical challenges of agility. Without any prompting, she will do things like climb trees, jump onto or over obstacles. The other day I had her up at the lab doing some nose work and she was searching in an area with a tall (4 foot?) lab bench. Well, she decided it would be easier to search from up there after finishing with the floor and just hopped up, to my surprise! Once she knew she could do it, she proceeded to do it again several more times. She has also climbed a tree (dog walk?). I notice an arousal when we arrive at an agility field/facility that I don't see in most other settings. That is how I know.
Poor girl hasn't gotten much lately as we've been taking a hiatus, but I'm hoping to do a couple of classes or private lessons over the winter.
Tara NW1 CGC - GSD 2008
Suli - DSH 2006