The defusing skill becames less useful as you increase the game difficulty setting: keeping on using the defusing skill could eventually succeed, but i suggest you to use the telekinesis spell.
The repair skill is not an automatic skill, you have to apply it to the items you want to repair. Again, sometime it fails, sometime not, keep on trying...
As an advice, do not repair your equippement gear, have the blacksmith do it for you (you loose durability points, you know), only repair items you're going to sell.
Malleus