"Stopping the tide coming in" is usually a reference to the English king Cnut (or 'Canute') who legendarily made his courtiers carry him to the sea:
> When he was at the height of his ascendancy, he ordered his chair to be placed on the sea-shore as the tide was coming in. Then he said to the rising tide, "You are subject to me, as the land on which I am sitting is mine, and no one has resisted my overlordship with impunity. I command you, therefore, not to rise on to my land, nor to presume to wet the clothing or limbs of your master." But the sea came up as usual, and disrespectfully drenched the king's feet and shins. So jumping back, the king cried, "Let all the world know that the power of kings is empty and worthless, and there is no king worthy of the name save Him by whose will heaven, earth and the sea obey eternal laws."
> When he was at the height of his ascendancy, he ordered his chair to be placed on the sea-shore as the tide was coming in. Then he said to the rising tide, "You are subject to me, as the land on which I am sitting is mine, and no one has resisted my overlordship with impunity. I command you, therefore, not to rise on to my land, nor to presume to wet the clothing or limbs of your master." But the sea came up as usual, and disrespectfully drenched the king's feet and shins. So jumping back, the king cried, "Let all the world know that the power of kings is empty and worthless, and there is no king worthy of the name save Him by whose will heaven, earth and the sea obey eternal laws."
From https://en.wikipedia.org/wiki/Cnut#The_story_of_Cnut_and_the...