Devices, equipments, lubrican… | Retention Plugs... Anyone? 1/1

I've read a lot in these pages concerning inflatable nozzles, but wonder if anyone has had experience with just a passive 'plug' to help hold enemas for an extended period?

The Optimal Health people offer two: one that is sort of a 'memory foam' device and apparently conforms to the topography of the rectum, but is somewhat fragile, and other that is more rigid and impervious to oils. Both can be seen here:

http://www.optimalhealthnetwork.com/Enema-Implant-Kits-Syringe-Enema-Retention-Plugs-s/1033.htm

I'd like to find something that would be an aid in holding-in solutions even during mild cramping, but don't want an inflatable device. It wants to be something that can be worn under clothing. Suggestions and recommendations most welcome, please.