If you are maintaining the dome properly, by making sure there is always water on the floor of the dome,
most cloning problems are the result of too much/too little moisture in the pellet/cube. Take one of your failures --
can you pull the cutting out of the pellet with little or no resistance? If so then I'd bet you over-watered the pellet.
You can check and see if the stem is dark where it meets the pellet. That's a sign you got the clone too wet.
Try watering clones from underneath. I have my pellets in plastic cups with drain holes drilled at the bottom. I nest
that cup inside an identical cup with no holes. The nested cups sit in the dome water and every other day I seperate the cups
and dip the inside cup into some water. Lets the cutting soak up water from the bottom and stimulate root growth. I mist the leaves 3-4 times a day.
Good luck, BigSteve.