jack russell shih tzu cross breed

Question
"We have a Jack Russell Shih tzu cross. It is a one year old neutered male. His name is Alfie, everyone loves him and he is people friendly....Most of the time! I have grown up with a pure breed Jack Russell and my husband has grown up with Three Jack Russells and one Rott veiller.
Alfie always wants to play and when we tell people to leave him because he can be temperamental, they can't believe it. He seems so friendly.
When he bites, there seems no real reason for it. He can come up and want to sit right on your lap. You might stoke him and he'll growl at you! We tell him off and put him out in the garden. My husband has smacked his nose and really shouted at him in the hope that he won't carry on with this behavior. This obviously hasn't worked. He has bit my 11 year old daughter, we felt this was because she kept picking him up so we stopped this. Now he has gone to bite her friend who he went and sat with but sort of growled and snapped at her. (no actual contact, but probably because she quickly moved.)
He was in the car today as we were driving out to take him for a walk. he was getting up and down from the passenger seat to the kickwell. My husband said come on boy get down and lightly tapped the seat to gesture to the kickwell, (floor) and he bit him just breaking the skin. We were stationary and he was in the car alone with my husband.
He is very protective over his bed as well. He doesn't like you to move it and we leave him alone when he is in it as it seems to stress him. We used to have his bed by our dirty washing bin and when my husband went to put his socks in it he would really growl at him.
Since we have had him we have moved 3 times whilst we were building a new house. I thought that maybe this is why he is possessive with his bed.
We love him so much and it would break ours and our daughters hearts to let him go to another home but we are concerned that we are not being responsible if we keep him. Especially if it is just so we don't upset our children when he could end up biting them quite badly.
We have spoke to someone who has said they may want to take him on to live on their farm, They do not have young children but do have another dog. Please help us by offering some advice we are desperate.
Many thanks for your time"  

Answer
I am so sorry to hear about your dilemma. It sounds like you have tried everything you can on your own.  I ,personally, would take your friends offer to take the dog to a farm.  I certainly would not want to hear from your next email saying the dog bit my daughter OR my daughters friend so badly that they will have a scar on the face for life.  This is what happened to a friend of mine who was NOT going to get rid of her dog because of biting.  NOW she has to look at her daughters face everyday with a huge scar on it and the dog put to sleep.  Its NOT worth the liability when it comes to kids.  NOT to mention in the sue-happy world we live in today. Obviously the dog will bite anyone and thats NO way to live for 15 plus years.    
 If your friend can't take the dog DO NOT......PLEASE DO NOT place it in rescue.  You are just passing the problem to someone else.  In this case the kindest thing you can do for him is to put him down. It probably would be better to say to your kids that the dog did go live on that farm.  Cold hard facts don't need to be told to kids....they grow up to quickly as it is.    
 Sorry....I didn't have anything better to say.  
Good Luck,
Tammy