Bondage in most healthy relationships id say is more in the mind than the physics. Ofthen when im tied up og i tie up a sub, getting loose if left unwatched would be pretty easy.
Not allways so but the point is, that really you dont have to use real handcuffs real padlocks and so on.
Theres plenty of slipknots and safety cuffs out there thatll allow for a feeling of restraint but not actually render your wife helpless. Pretty much a mechanical safeword really.

Now it will take some study getting this to work and ill gladly review any solutions you come up with and possibly do a bit of experimenting at home.
This safety bondage issue is most likely relavent to alot of new submissives and dom's training them.