I watched the earlier video of Gnash tracking too, and I think you were creeping on him. This spatial pressure can rush the dog a bit IMHO. He handles it really well, and it may not have effected him at all. Just something I noticed.
How does he do if you back off on the line and give him some space?
When a dog saves the life of a man, it becomes clear that partnership knows no bounds.
Fama - T.E.D.D. OEF XI-XII (GSD)(RET... )
Marshall - T.E.D.D. OEF XII-XIII (Lab)(SF EDD)
Lucian - Med Alert (Cane Corso)
Pud - the old man (Pit x Lab)