A Bob 'Ole

Dry stone walls are great for dividing up fields, and keeping livestock where they are supposed to be.  However, when a field becomes overgrazed and the livestock need to be moved to an adjacent field, the standard gate is a bit overkill, particularly when the livestock is small - i.e. sheep.
Hence we have the Bob 'ole - to allow the sheep to 'bob' through into the next field.  Sometimes called a Sheep Creep or a Hogg Hole.