Oh, I can't keep up with him physically! Luckily, he's fairly calm for a Border Collie, so that's not too much of a problem; I can generally settle him with ten or fifteen minutes chasing the tennis ball. I had to teach him what balls were for, and it was a good thing I did! He'd probably have difficulty if I was still working and he was alone all day, but he really enjoys having a human at his disposal at all times.
He does always need something to think about, but I don't mind that. It's fun to think of new games and variations for him. His main job is taking care of me.
Also, we go to dog club two or three times a week, which gives him lots to think about. I do love having a training club nearby. It's fun for both of us, and I don't have to purchase and maintain all that equipment!