Best path between raised beds to deter slugs?

I wouldn't go to too much time and trouble trying to deter slugs on your paths. Its the ones on your veg beds that are a problem. The slugs and their eggs are in the soil of your beds, Its a bit of a myth that they only venture onto your beds for a feed then wander back off again.

I concur with DMH - multi-pronged attack. I use beer traps to great effect - v cheap beer (90p Asda for 4 cans) in jam jar or yoghurt pots, occasionally with something to keep the rain off overhead, they need to be an inch or more proud of the ground so beneficial beetles don't fall in. Beetles eat slug eggs.

Coffee grounds are good for point defence. Coffee shops are usually happy to give their spent grounds away.

Nematodes are about £12 a go and you have to use them as soon as you get them and when the ground is warm enough. Try one application April-ish if you don't want to keep shelling out 12 quid; shows the slugs who's boss from the get-go.

Leopard slugs are your friends too - they eat rubbish, not your veg - so don't kill them either.

I use a combination of copper rings and nematodes, which seems to work well enough to get a crop. Next year I am going to apply a second lot of nematodes in mid summer, as despite the lack of rain this year, my cabbages have been ravaged, particularly in August when the weather flipped to mediocre normal.