I'm not sure what you have, but my toy soldier collection was always kept in glass front cabinets with locking slinding doors. I used those slide locks you often see in stores - about $10 each. If you don't go into your cabinets much, or you cannot lock your cabinets, you can buy security stickers (@ $2 each) from your local locksmith that show a door has been opened. This discourages "browsing" but won't prevent theft.
Might also be a good idea to take an inventory, if you have not done so in a while. A friend of mine put all his stuff in one small bedroom and locked the door with a dead bolt. If you have specific problems or issues, consult a good locksmith.
Of course, I assume you basically "trust" these cleaners and they are bonded. Otherwise they all the time int he world and a secure environment to work on your security system.
Good luck!