What is the best way of attaching another cable?

Any advice or suggestions gratefully received.


http://www.kneesnet.com/acatalog/Kneesnet_Online_13
_Amp_Flex_Connector_355.html

http://tinyurl.com/apxdw

I am after a waterproof (immersible) version of this.
Any ideas?

(It is needed to join a pump cable inside a large water fountain)

I have seen the ones designed for SWA cable, where you pour resin into
them - Could I just use this? (The cable looks like 1mm flex)

Sparks...