Donal: INternal OB is OK under the rules, though it should be used sparingly. There are three reasons for internal OB: 1)safety, 2) make the player play the hole as designed, and 3) pace of play. For example, when a practice range borders a hole, making it out of bounds discourages the player form spending the time to lok for the ball.
Futher, internal OB can be in effect for a tee shot only. It cannot be in effect for a subsequent shot if it is not in effect for the tee shot on the same hole.
Three on one course seems a little much unless it is very cramped and therefor has multiple safety issues.
Jim,
I can accept your reasons 1) and 3), but 2) only confirms to me that the design is at fault.
I've had a dislike of internal OOB since I hit a drive on a gentle (135 degrees) dog-leg at Lurgan GC. I couldn't believe it when my playing partner said, "Oh, yes, that out of bounds". It destroyed my good round up to that stage.
My understanding is that to go OOB, you must cross the OOB line. With internal OOB, there is no closed line of OOB, i.e. the OOB is not a piece of land, it's just a line. So if you wanted to make a mockery of it, you could play backwards until the start of the OOB line and then play around the back of it. It sounds silly, but you'd be behind the line, although you would not have crossed it. This is why I believe internal OOB is bit of a joke.