Block paved path

I think I'd go for 2" MOT and 1" sand.

Sand itself is more than enough to support a pedestrian path but it is prone to insects tunnelling through it. I suspect they give up when faced with a layer of compacted limestone which then stops them getting to the sand. Only a theory mind - but the bit about tunnelling through sand is right as you only have to lift a paving slab laid on sand to see who's living underneath.

In my experience, you don't even have to lift a paving block to see that, as there are always little piles of sand at block joints, where the ants go in and out. I kinda think they'll get in whatever happens, in the absence of something toxic in the sand.....

Now there's a idea....;-)

My block paving was laid, by experts, a la paving expert. 20 years later, tree roots have disturbed enough of it for it to need relaying.

We did that for many year with white ants but that got stomped on because it was so persistent.