Hey I am making a multiplayer map and it includes magical blocks that will give you certain effects for example:

> /execute @p[r=10000] ~ ~ ~ detect ~ ~-1 ~ wool 15 /effect @p
> invisibility 12 3 true

 which gives invisibility when the "nearest" player stands on it. How can I give the effect to the player who stands on it, not just the nearest player to the commandblock giving the command?