I've had my belly button pierced twice. And sadly both times my body rejected it. The first time i blame on the piercer. they pierced it off centre and at a bad angle (my mistake at 16 for going to a place that does not have proffessionally trianed piercers) I had it for about a year before I took it out as it had pushed itself out to just a think layer of skin. 

the second time I went to a professionally recognized piercer and sadly even though it was done properly my body rejected it again. I've now attributed it to a slighty metal allergy. I've had other body piercings and as long as i use higher quality metals(gold) I am ok.

all of this talk makes me want to go get it done again though…..maybe third times the charm??? I'm not worried about scar tissue as my belly button is now also scarred from surgery from gallstones.