I'm sure there are folks here who can give better advice than I, but here are some tips which may help a little - based on my experience of using the 96 Deco a fair bit over the past week or so.
1. Try to take advantage of the 96's high chance (20%) of shots going astray. So keep your distance (close to, but within your max range), even if they outrange you, as it may just save you from getting splatted. Of course this depends on what weapon you're using, so be aware of your gun's max/effective range and accuracy relative to the 96 (or any other weapon for that matter).
2. When it comes to wall you need to put pressure on the 96 user when possible. It costs a fair amount of ink to use, and the gun itself isn't very economical either. With that in mind, you want to harass them into having to re-deploy the wall sooner. Even it's just a few shots, or better yet a burst/splat/suction bomb, it'll have a noticeable effect on their ink tank. Depending on the location/placement you may even be able to chuck bombs over, which can really cause them trouble.
3. Try not to automatically retreat when you see a 96 appear and quickly put their wall up. Of course this doesn't mean you shouldn't reposition yourself. My point is that if you withdraw completely the 96 will probably just ink all the space in front of their wall, push into the newly captured territory and put a new wall up. Meaning you're back to square one, except that they're now closer to you/your team/the objective.
4. Dealing with krakens takes a bit of getting used to. They key point I'd say is to try to be aware of when they do and don't have kraken ready to go. That obviously applies to all weapons/specials, and to be honest it's something I'm still getting to grips with, but if you know in advance you can be prepared. Burst bombs seem to be particularly good at knocking back the kraken, so try to practice that now and again if you're up to it.
5. If you are hunted by a kraken, lead them on a merry chase into your territory. Less aware players will not pay as much attention to the duration/surroundings and end up waking up alone in enemy ink with you and/or your team around them. Better players will know not to make chase. Of course this advice may be moot if they're stacking swim speed up...
That's about all I can muster of the top of my head. Hopefully it helps you somewhat. If not my apologies, I'm still learning too :-)