Clearly we aren't communicating effectively. I'm good at not communicating effectively. Let me try to explain it another way based on the assumption that your current row and the row before it are dc, ch across.
Say you have 10 dc in your current row with chains in between them, the previous row is the same. If you work to the end without decreasing you will end with 9 dc, ch, dc in turning ch of the previous row. So far so good?
Now you want to dec 1 st so you - work 8 dc, ch1, Do not work the ch as you have previously. Your hook is in the top of the dc. Work a double treble in the turning chain of the previous row (where you otherwise would have a dc) and when you complete it your yarn will be exactly where it should be.
I really hope that makes sense. Who is the crochet expert that isn't around much? MGM? Maybe we'll get really lucky and she'll see this and come to our rescue.