Preventing power levelling?

One of the problems I've come across in the past is players who group their low level characters with higher level ones, slay multiple creatures and gain a proportion of the experience for essentially doing nothing. There are, however, two sides to the coin so to speak - players who reroll their characters and want them back up to where they were previously.

But, I would like to hear if anyone has implemented a system where characters must actually participate in a fight in order to gain experience from it. I had put in a system which attempted to determine what percentage of damage you did to a creature and then allotted you that same percentage of experience after the battle - it worked to a degree, but it wasn't 100% accurate and that's what I was striving for.

Do others perceive this sort of thing as a problem? Has anyone come up with a novel solution to prevent it?

I went with a scale of diminishing returns for killing mobs more than 10 lvls bigger than your character. I *think* the public release of the DoT codebase has the xp scale I cooked up but if not I can find it easily enough. Still not a fool proof system but it works reasonably well for what I needed to adjust.

a system were xp is calculated by how much damage wouldn't work because clerics who heal would lose a lot of xp.

I know this is an old thread, but to stop powerleveling, i have put in afew things to slow the process, the main one is, if you didn't damage the mob, you don't get any xp, and you get xp based on your % of damage done to the mob.

So if you kill a mob 90% of the way, and you are forced to flee, and someone else kills it, you still take the majority of the kill, where-as, if you only do that 10% of the damage, and everyone beats the crap out of it, the xp is ultimatly changed.

Another method to slow powerleveling is to force them to return to a place and infact, type 'level' or something, which oddly enough, i do in my mud.

These are basic little things that one can do..