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Use electromagnetic door locks, can be had on e-bay for as little as <$20.00. Glue a eye bolt to the outside of one or both to make attachment points. they're 12v so use a cloths pin with a contact on one jaw and a strip of metal as a contact between the jaws as your emergency release.

I use 2 extra large condoms (1 inside the other per boob a single breaks too easy), add about a measuring table spoon of water adsorbing crystals (get them at planting stores). Add the amount of water needed to reach the size you want and tie them off (hard, they're slippery) or use a small zip tie ...