Erase Rune Ruling
I am going to rule that erasing runes is basically the same as disabling a trap.
If you exceed DC of the rune with a caster power check (level + int bonus), then you erase the rune.
If you fail by 4 or less, then you know that you failed and can try again.
If you fail by 5 or more, then you think that you succeeded and can't try again unless you discover the rune is still active, with a detect magic or new sense rune (at a penalty of -2 per failed attempt).
Also, I am going to rule that you need line of sight to erase another person's runes, though you can erase your own so long as you know where they are (so you can't erase an applied rune on a person, unless you know where they are or can see them).