Internal OOB markers should never be removed, even if playing the hole where they aren't marking the OOB. If you move them then you may be at risk of changing the dimension of the OOB area for the hole where the markers are relevant.
as has been said they should be classed as immovable obstructions in the local rules
a) In or over the trench on the flood bank when playing the 6[SUP]th[/SUP] hole
b) During play of the 5th hole the stakes and trench identifying and defining the out of bounds on the left of the 6th hole are deemed to be immovable obstructions.
