Fence me in

It's springtime. The TMI household has two small children, one of which is extremely mobile and moderately disobedient.  Our property backs up to the wetlands area and we are near a busy train rail.  Naturally, our thoughts are turning towards getting a fence. 

To see what was available, the Little Guy, BabyGirl and I did some recon in the subdivision to see what fencing styles are out there.  Here's what we saw:

I think the last fence (last two pictures shown) is the winner.  The simple, straight lines are attractive, and I like the cap on top.  Now, the Big Guy and I have to decide on things like height of the fence (I think 4' is fine, he would like 10' topped with barbed wire) and placement.  I'll be getting some quotes from various companies over the coming week to see if this is financially possible for this year, or if we could do it cheaper ourselves.