Changing behavior

Question
I have a 2 yr german shepard male. We got him at about 4 mos. old for a akc registered kennel. He was the only pup  of the litter left.
He has always been  fairly active (maybe a bit over active), but playful and healthy. Loves to run for thrown balls and just about anything we throw for him. He is very upset when the children ride bikes, sled in the snow or when I mow the lawn especially on a riding mower.

We installed a invisible fence over a year ago and allow him full use of a 1/2 acre surrounding the home. We do have another pet, a 6 year toy poodle (spay,female), who we had when we got our shepard.
The poodle is allowed in the first floor of our home and the shepard has always been allowed to go as far as the attached garage, on occasion he slip into the home but isn't allowed to stay for any length of time.

He has a pet pen in the garage for over the evening and when he needs, for discplinary action. But  that is only after the "NO" lecture. The Shepard is playful with the poodle (sometimes rough), but the poodle never has enjoyed in the same.

The shepard has always been very attached to who ever (in our family), is out with sometimes annoying because he won't leave you alone for a second!

I have noticed recently he seems intimidated by me. All I have to do is be seen. He crouches with ears back and tail under and won't come to me, I have to approach him and he'll roll on his back for a belly rub.  I toss a ball or toy every morning before I leave for work and look to greet him when I return, He always responds to me without any aggression but more the opposite. After we get past that he's ready for play.

We have 3 children age from 9 to 13 and he has been good with them and most everyone up to a couple of weeks past. When my middle child was returning from the neighbors with the neighbor (who is at our home several times a week)the dog grouled and  jumped at them. This weekend he jumped at our guests without biting, and has done this again to the same and othes guests (adults or children), he's not prejudice. But his method is concerning to me. For example, lately when a vehicle enters the driveway he will lay down in clear sight, when the person gets out he'll stay until they walk past him then pull this jumping stunt. Yesterday (Tuesday), he took this to the next level and bit a 13 year old guest as she was entering our home. He did this as my two younger children were with her and trying to comfort & restrain the dog. He then was put in his pen, when my wife came home she walked him and returned him to his pen. When I came home  I went to his pen he was normal, my wife walked into the garage to see us and he became very aggressive toward her bark and growl. He quickly backed off (still in the pen), but then my child came into the garage and he was very aggresive to her also.

I then leashed him and walked him again but  he didn't seem interested in staying out or playing. Walked him again this morning (on the leash, and again he wasn't playful. Possibly the leash?

I did find a very large bee hive in the corner of our lot & his area, ,my son said he was  nosing in the area yesterday before the incident and he does find them of interest but I checked the dog for stings and abbraisons and found none. Maybe I'm just looking for excuses for this sudden bad behavior.

Your thoughts are appreciated.

Answer
Hi Anthony,  You definitely have a potentially dangerous situation on your hands.  Has anything changed in the dog's or your life in the past few weeks?  It can be anything that may be really minor to you but very major to the dog.  Since the incidences are progressing, that is a very dangerous sign.  Did you meet the parents?  Let me know the answers.

Dawn