@Lawrencelot: That depends on what style of Fox you play.
If he approaches a lot eat his approaches with WD back ftilt, nairs out of shield, retreating SH fairs, utilt when coming from above and tons of needles and bairs.
If he plays campy either charge needles and make sure that they hit so you make up for the laser damage or run up to him and then watch what he does in that sitaution usually.
At first you can WDback for example to figure out what he does (since you stay spaced and in case he rolls behind you you get a grab)
If you notice that he jumps a lot when you run up to him simply SH fair (which can be cool especially at higher %s)
If he dashes away you can often get him with boost-grabs.
Or run farther and dashattack or dtilt or dsmash
or dash cancel and ftilt ... that's cool somehow
Edit: if he's very smart with mixng up defensive and offensive style ... you have a problem