The no dig winter lettuce bed

Step 2:  pile some year old very rotten manure, some free compost from the council and some horticultural grit and mix well.
Step 3:  spread out into an even layer several inches deep ( I need to check the best depth, but have more council compost if needed).
Step 4: put the cold frame in place.
I'm wondering about getting some wildlife friendly slug pellets before the lettuce go in.
Water butt update: No leakage around the crack and the  tape is looking good, but it now appears to be leaking around the tap and that may be more difficult to fix. Now emptied and drying off again.
Extra: guess what is peeping through?  Just one here, but I counted 9 showing this afternoon.