I've had somewhat similar constraints from time to time and they seem to be temporary.

One aspect of lucid dreaming that I always avoid is "trying", wilful intent doesn't seem to work very well and I slip out of lucidity fairly quickly. So in this instance, "trying" to get out of the yard would blow the whole thing.

What I've done instead is to come up with experiments within the constraints of my environment, many of which I've actually come up with in the days prior to the actual lucid event. Here are some of the experiments I've tried when I'm in a limited field of experience:

-can I look down and see my own feet or hands?
-can I hold my hands up and study them? What do they look like?
-can I rotate (sort of like a gyroscope) or make other types of motions or movements that I couldn't ordinarily pull off?
-is there anything detailed around my room (yard)?
-can I lob something? Will it break?
-can I lie down?
-is anything "sexual" possible?
-how many details of my waking life can I recall? --including what side of the bed am I sleeping in?
-is there a book or anything else I can read? Does it have pictures?
-can I speak?
-is there a fence around my yard? Can I walk into another room or in some other way ambulate (again, without "trying" to escape any perceived confines).

I just read a posting that talked about spinning like a top a little bit, and when you come to a halt, the scene has changed. Hopefully I will be able to recall this when I'm in a lucid dream. Sometimes I have a little trouble forgetting details like this, but I'll usually remember what it was Iwanted to do after a few episodes. The trick, again, is to avoid "trying".

Anyway, hope this helped.