Some practicals are dangerous, but necessary if we are to teach the syllabus thoroughly.
Dissections often cause palpatations among science teachers – there is a glut of things that can go wrong. Stolen equipment should never be one of these.
Mark all of your dangerous equipment (scalpels, micro-balances, syringes etc.) with a number in permanent ink. Have a corresponding numbered list. When you hand out a scalpel, make a single person responsible for it. They sign their name next to the number of the scalpel and it is not to leave their sight.
If the scalpel does go a-wandering, you know who to go to, and who has to frantically search for it while the rest of the class wait behind their seats.