You can get pretty good tension using the terminator shown below. You take the free end of the lashing and tie it to a halyard - in my case a 2-1 halyard. Tension it, secure it and then take the remainder of lashing and half-hitch it around itself.

The soft-hanks are unlikely to come loose. They fit pretty snug, self tension when pressure is applied and have little rubber grommets that also secure them.

Paul L