I have always been a big fan of playing a strict man on man system in our defensive zone. It is a system that certainly demands good skaters and dogged defensive players. It is also a system where teammates must have trust in one another to do their own job defensively. It's the easiest defensive zone coverage system EVER - "find a man and don't let him score". But, it's a difficult system to perfect, especially when every player on the team has to buy in AND play it well.
In a long season, I have found the best approach to defensive zone coverage is to play man on man for the first half of the season and then play ANY type of zone defence for the second half. This is why.
There are three skills that players need to learn in any kind of defensive zone coverage system. 1) Playing a puck carrier (one on one) going to the net, 2) covering a player in front of the net and 3) covering the point. No matter what system your team is playing, your players must practice these three skills on a regular basis. And, playing man on man in games with help them gain confidence and really test them to be able to execute the skills all of the time.
Then, once you move to a zone type system, players will not only have the skills to play in every situation presented but they will be thinking "where is my man" inside the zone they are covering. Often with zone defence players are simply content to be "in the neighbourhood" in their zone and they aren't focused on covering the man in their zone.
A couple of key talking points I like for the three skills:
1) Playing a puck carrier (one on one) going to the net - "stay on the balls of your feet - like a tennis player", "watch the chest, not the puck", "use your hands"
2) covering a player in front of the net - "defensive side", "take away the hands - not the stick, shoulders, etc."
3) covering the point - "stick around the waist", "don't let them beat you into the net front area"
These are all crucial individual tactics that must be mastered in order to be a complete player.