Nut and Bolt for one blade on cutter deck keeps working loose....why?

[Peterplocket]

Hi everyone,

I have a fairly old Husqvana riding mower. A few years back I replaced the worn out cutter deck. The replacement deck is now about four years old and one of the blades' nut and bolt that secures the blade to the deck keeps working loose. Why this should be, I can't imagine.
If anyone has a solution, or has had experience of this happening, please write and let me know your thoughts.

 

[mechanic mark]

Use a self locking nut & blue lock tight. Vibration, make sure blades are balanced.

 

[Peterplocket]

Use a self locking nut & blue lock tight. Vibration, make sure blades are balanced.

Cheers Mark. Thanks for your advice.
Since writing, I took off the top nut and found the bolt that passes through the bearing to be quite worn, so maybe replacement of the bolt would be a good idea and bearing too, maybe? Until then, I'll take your advice and try to find a self-locking nut and use some blue locktight. Thanks again.