Psalm 129 and Ploughing furrows

In agriculture it is good to get the seed deep into the ground if it is going to flourish and initially people would use hoes to create holes in the ground into which the seed could be scattered. Early on it was realised that a more efficient method is to create a furrow in the ground, an extended hole, a sort of trench. This is done with a plough. Here the psalmist says it is as if the enemies of God's people have been ploughing furrows into the backs of the people. He says that the furrows are long because it has been going on a long time - from the slavery of Egypt to the opposition of the Canannnites and especially the Philistines through to - and we do not know when this psalm was written - the carrying off of the people of the northern kingdom by the Assyrians and then the southern kingdom by the Babylonians.