hmmm....Are you for real???
How much does this Yorkie weigh??? Is he neutered??? Males that are left intact have "urges" to run for females in heat...
I think it is VERY unsafe for a Yorkie to be "allowed" to run free thru the fields/farms, etc...He could get seriously hurt, or killed or attacked by another animal...
I suggest that you put an expen around the door area, so he CANNOT slip thru when the door is open. Here is what I have, it opens up and you can "block off" areas (like the door)
Walmart.com: North State - Superyard XT Portable Playard & Gate: Gear
Now for when he should go outside. Can someone take him for a 20 min walk everyday ??? With him being in a harness and leash????
Or can you build an outside pen for him to play in when it is nice outside?
...again, if this is for real, he SHOULD NEVER be allowed to slip thru the door and run free outside...PLEASE use more caution