And, with all his fragile old strength, he hung on; grinding the outworn fangs further and further into the sensitive nose of his squealing foe.
This stopped the sow's impetuous charge; for good and all.

With a heavy collie hanging to one's tortured nose and that collie's teeth sunk deep into it, there is no scope for thinking of any other opponent.

She halted, striking furiously, with her sharp cloven fore-hoofs, at the writhing dog beneath her.
One ferociously driving hoof cut a gash in Lad's chest.

Another tore the skin from his shoulder.

Unheeding, he hung on.