I would imagine that there's seldom need for Ike to approach here. A simple back jumped fair can prevent most of ganondorf's approaches, especially since he is very easy to hit with it.
Even though many of ganondorf's attacks are surprisingly quick and powerful, they're open enough to get punished by an nair if quick enough. Only a ganondorf with superior prediction, spacing, and knowledge of the matchup would even hope to win. If ganondorf gets knocked in the air, I don't even need to get close. Just jump back and fair, since there's little hope of ganon doing much. There's no point in going close here at all with Ike's range and ganon's speed.
Off the edge, as previous posters before me have gone through before, walk off dair prevents recoveries directly below. I recommend only using walk off fair at medium to higher percents to prevent any accidents. Once recovery from below is sealed, there is little hope left for ganon, since his forward B can be tilted. As far as I know, ganondorf can't do much with edgeguarding Ike, since there's a higher chance of ganon getting gimped instead.
Looking out for are his deceptively quick tilts, his down air, fsmash, quick dash attack, and forward B are a must.