ok - if you're serious, be careful.
A penile implant is used solely to treat erectile dysfunction, and is only now used when viagra or cialis aren't options.
Implants of stainless steel objects can be done for fashion, but seriously... would you?
However, penile extensions are common, consult a plastic surgeon. Involves a serious operation where a ligament in your groin is slit to allow more muscle outside the body.
As for injections of fat to improve girth - they're apparently rubbish as the fat is reabsorbed eventually by the body.