Was watching A Bridge Too Far today. There's a part where Polish troops are making a night crossing of the Rhine in little rubber dinghies, pulling themselves along by ropes. The Germans entrenched on the far side of the river wreck the crossing with machine gun fire and heavier ordnance.
Not that I'm supporting the Germans, mind you, but the US border could learn a lot from that movie re: keeping people from getting across rivers and halting advances...