Any of the Mtronics Viper Marine ESC's have failsafe and will stop if radio signal is lost. They are available in 10A, 15A, 20A, 25A and 40A. You need to mount them so that air can circulate round the side away from the wiring. They will stop if they get too hot.
The Mtronics site
http://www.mtroniks.net/index.asp have some Ex demo or test at slightly cheaper prices and post free otherwise any of the model boat shops will usually stock