"That's a wise precaution. I have mane and tail hairs from all of our horses." He nods at her idea. "And yet, if a colt escapes on foot, they can be found easily enough with tattletale. One that can fly... if not found in time, what then? He may happen into a sky trod, or unfriendly chimera. Or even be sighted by a mortal. And I need not beg you to imagine the results if noticed mid-air." Shaking his head.
"I had thought, if our Hostler is obliging, a harness that may be..." He looks at the nocker appraisingly. "Weighted, perhaps, would be the mundane thought. But surely something more elegant. Perhaps a binding that prevents him from leaving more than a certain height off the ground? If there was a way to affect that magically... he could leap and cavort, strengthening wings, and yet still be prevented from taking off. Maybe even a way to adjust it over time as he grows both in strength... and more slowly, in wisdom. Miss- ... Willy. What might you suggest?"