What is eating my basil?

My beautiful basil is being attacked by something which lives many irregular holes inside the leaves. Its not an animal must be an insect. I've put stuff down to get rid of slugs to no avail. Any advice is appreciated. Any anti slug measures which could be would be a great help.

Here are some images of slug damage and pictures of slime trails to make sure that's what you're dealing with. In the past, I tried Sluggo, which is a bait made from iron of some sort (so it breaks down into the soil) and which works well, but it comes in huge amounts and I don't want to buy so much for my tiny garden.

This year, I've been crushing eggshells and throwing them on the soil, and dusting the plants with wood ashes, which apparently are a deterrent; I don't know if it's working or not, but the holes seem to be fewer. There's the old dish-of-beer trap method, which works if it doesn't rain overnight (you have to throw the slugs away) I'm mostly just hoping that at some point the weather will dry out and so will the slugs.

Sluggo uses ferric chloride (aka iron(3) chloride), which is toxic to slugs. Slugs feeding on tender lettuce usually ignore Sluggo. Sluggo dissolves readily in rain or water from overhead sprinklers.

I have never had a slug problem with basil, but we sure have a lot of them in our bibb and romaine this year. Sparrows can be a problem with direct-seeded basil here. The damage is on the outer edges of leaves. Bird netting until the plants develop more and tougher leaves is the solution.

Edit: Sluggo uses iron phosphate as the active ingredient. Some other slug baits have used iron chloride. I should have checked my can rather than relying on memory. Sluggo can says "Remains effective after rain or sprinkling." Not very in my experience.

Yes it does look like that. We have not seen slime trails. On the weekend we took the basil out of the garden and moved it to some large pots on our patio hoping it will recover.

We had to move the basil from the garden to a giant pot on the patio. No more holes in leaves. Its really big. I hate when things attack your garden plants.