Something we do regularly, both at home and at the Rescue, is to carry out a simple health check on all our bunnies. This helps us spot problems early and gives us a perfectly legitimate reason for cuddling everybun. :-)
I think I'll save the details of the sort of things we look for for a future post, but one thing we almost always check is their weight. A change in weight can often be the symptom of a real problem, or it can just be an indicator that we're feeding them too many treats! Either way it's a good idea to monitor it and take appropriate action when necessary.
But you're probably not going to want to shell out large amounts of money for a veterinary scale. The human scales are often not sensitive enough, the kitchen scales are often too small. So here's a handy tip: A good cheap solution is the "luggage scale". They are available very cheaply online, and with the addition of a ceiling hook/chain and an old shopping bag (NOT the plastic variety!) you've got yourself a perfectly affordable way to monitor your bunnies' weight!
Now all you have to do is persuade them to climb into the bag...
DISCLAIMER: We are not responsible for your carelessness. Think practically - DON'T hang your bunny 6 foot off the ground. Lifting a tubby bunny over your head could end badly for both of you! Add a sturdy chain so the bag hangs lower, put a chair under it so if something happens the bunny won't fall far, and test the strength of the whole thing by weighing something non-sentient first!