You have to be really careful when lifting the skin...if it starts ripping it just doesn't stop. You made the right decision to stop, but I must say - if you can get the rub under the skin it is worth the time it takes!
If you are trying to raise the skin for butter, spices, or some fancy type fried duck, a lady friend taught me long ago to use a rubber spatula. It doesn't tear the skin and a good silicon spatula has enough "push" to get thru the layers.
I never think on it, but it works when my fingers get too tight. Especially on the leggs.
She said she had seen people use an air compressor to blow the skin up like a baloon, I never caught her in a lie so.......