Well, there is no need for a hard hitting opponent if you have some experience in restoration and have some spells to go with it, and a lot of restore/regenerate magicka potions, and mage robes, magicka regenerating rings, amulets, enchanted gear, and so on...
you have to have the "Respite" perk in restoration, and a higher level healing spell and a heal other spell, then you find an opponent with a lot of hit points but not so much damage output.
You keep bashing the opponent until you run out of stamina, then you heal yourself, so that your stamina replenishes, and keep bashing again, until the target is near dead, then heal it, and continue with your power grinding...
This way, you gain Block skill faster than when you just keep blocking attacks, and you do not have to find hard hitting opponents, and also advance your restoration skill as well, which is another very useful skill.
But you really have to have the "Respite" perk first.