Skin Deformation with Automatic Weighting

I never had any problems with the Automatic Weighting feature when rigging… until now.

My character’s pants are too big for the armature. As you can see, in the picture below, the green dotted areas are where most of the deformations happen:

How can I ensure that the green areas of the pants become a part of the bone?

EDIT: As you can also tell in the picture, the bones in the shoes were also once a problem, identical to this. I fixed it by making a second bone, so they cover up more space. I tried doing so with the pants, but to no avail.

Possible solutions in order of ease:
Weight painting.
Vertex group editing (add those verts to the thigh group.)
Additional bones (for instance in a ring around the hem, all parented to the thigh bone)
Envelope bones, adjust the influence, re parent the armature using ‘envelope weights’.

I tried Weight Painting…
the ankle makes it hard to be precise.

It seems as though no matter what I do, the deformation always occurs at the same location.
I found out there were loose faces inside the leg, deleted those but nothing changed.

Out of frustration, I went ahead an painted the entire leg red…
I also painted other parts of the body by accident. After fixing those, everything should be alright.

Thanks, DruBan!
Didn’t know about Weight Painting until today.