Because you're saying He created it--unless you're attributing the glory of Creation to Satan, in which case I can only say "DON'T YOU BLASPHEME IN HERE! DON'T YOU BLASPHEME!" (with apologies to Aretha Franklin)
God created all the creatures. So some died and left fossil remains. How does that equate to God planting it and being a pratical joker?
And, No, I'm not attributing CREATION to Satan by any stretch of the imagination. I don't know where you got that from. God created. Satan can't create but he can change. There is evidence in Scripture that clearly indicates that Satan can manipulate the physical world. How do you know that Satan didn't manipulate stuff to make it appear that way?