This is what experience comes from.

The wound is a couple of years old and came from a shoe that came loose and then got stepped on and the toe cap crushed into the white line. A traditional farrier has been treating the hoof since then but as you can see with absolutly no luck. The owner was very cautious and didn't allow the trimmer (who happends to be one of my first students) to trim through the waterline.

Here the owner gave up and gave the trimmer free hands since nothing got any better. This is the first trim that starts to remove the pathology.
The marking on this hoof is made for measuring the growth and as you can see on the picture below the growth is at least one cm/month.  
Look at this!
A wound that has been there almost from the beginning of time starts to disappear.
Here we are today. Just about perfect. I'm proud of my students. This one in particular.
Trimming job done by Kent Wiberg.