vanishing carrots

[nemo]

3 packs of carrot seed sown each time they have come up but they vanish i have surrounded them with a copper barrier then with an extra barrier of slug pellets with the copper they always come up about 10 mm high but they all disappear over time what else can i use. i have a big crop of strawberries near where the carrots were sown and the copper worked well only a few had slug damage
I REALLY NEED ADVICE ON THIS ONE
regards nemo