I personally would use the rotted leaves for something else, my own seed compost maybe, or I’ve just used a load to mix through with a bag of peat free compost & my own made compost plus blood, fish & bone to pot up strawberries into hanging baskets, some for the tunnel & some to hang in the fruit cage. I’m hoping it will be ok
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I just put the fresh leaves in a wire mesh container to rot down, then about once a year tip it out & mix it up a bit as the top ones don’t rot so well.
If yours is well rotted it shouldn’t harbour slugs any more than your cow manure or soil will. Slugs are attracted to wet hidey holes & unrotted mulches as a source of food.