Disappointment

I was really disappointed with one of the supervisors today at work. He blew out today and even though I realised yesterday that he was not totally switched on, I didn't quite realise until today how little work he actually did.
He is the youngest supervisor there at the moment and a bit immature and unprofessional, but I know, if he focused that he can do the job well.
It is difficult getting him to realise that work is a serious business. I am worried because if he messes up then it could affect the whole security team. We have been getting a fair amount of praise since the client moved in, but there are also a couple of people who want to make their names with the client and their own companies. These people have set their sights on the security department to be the stepping stones for their promotional aspirations and have already started sniping and picking faults on every single thing that the team do and have even begun to think that they can tell the facility manager how to manage the security team. Big mistake.
If this supervisor does mess up more than he has already then he could really muck things up for himself and for the rest of us. We are all deserving of a pay rise, which should have happened when the client moved in, but have to prove ourselves constantly to maintain what we have at the moment, let alone getting more. We have had to struggle with our employers up until now, just to get the rights that we were owed from when we transferred over from our original company, so it will be even more of a struggle to get extras. We aren't even being provided with the tools needed to do our job properly, yet are still managing to pull it off. If one person makes a mistake, especially a supervisor, it could prove disastrous for the whole team.
I need to find a way to make this guy take his job seriously and pull his weight fully, at all times. I just hope that I can manage it without pushing him the wrong way and making him not care at all. He needs to be chastised for doing such an appalling job this week, but encouraged because I think, if he took it seriously and thought of it as a career and not a job, then I think he could be really good.
Let's hope that I can keep my cool and not release the frustration that I felt with him today and can just provide the right push for him. I know I can be a pretty good motivator, it is one of my strengths, but only when I care enough and until this week I haven't really cared. I hope that I care enough now and that he takes note of this and responds to my attempt at nurturing him. On top of the fact that I know he has the potential to do the job I want to encourage him and turn his performance around because there are very few options for alternate supervisors should he stumble and fail. And all of our jobs are still officially classed as "at risk" by our employers.
Here's hoping that I handle it properly. It is probably the most pressure that this step up has put me under so far, the rest has been, dare I say it, fairly easy.