Larry - one other option to bait, and if a slide cannot be located... In the area of you val plantings, build a 10' to 20'-long "brush fence" that runs perpendicular to the shoreline. Leave a small gap (8") in the fence, located a few feet from the shoreline. In this gap, set a 110 Conibear (hinges oriented up and down) with its jaw-bars mostly submerged.
Rats would rather swim than walk along the shoreline. Forcing the rat to travel through the gap (and Conibear) might give you better results that trying to bait or lure him into a live trap.
Good luck.