As you progress in the game there will come a point where you have to dodge attacks which will drain your blocking meter as you use it to the point where you eventually will not be able to block anymore. Use the earlier fights to learn how to dodge more effectively so you are more experienced when you face tougher opposition. When faced with a slow opponent a good strategy is to dodge when the attack comes in not when they wind up.
Returning to earlier battles will give you the opportunity to meet challenges and earn experience. It is also a good way to accrue experience, silver and a few rubies and put you in better position to defeat a current foe that is causing you problems.