The light rail precedents we have in Canada both use fencing.
Here's as similar a locale as I can find in Calgary, on the Northwest line. Ignore the grade crossing and look instead at the barrier separating the road (think Richmond) from the LRT line and the fence separating the LRT line from the park behind (the Byron tramway park).
http://maps.google.ca/maps?f=q&sourc...,114.62,,0,2.9
Also in Calgary, the Sunnyside area has barriers, which are relatively tasteful as barriers go, but still barriers (again, ignoring the grade crossing, which we may or may not get):
http://maps.google.ca/maps?f=q&sourc...98.93,,0,11.81
From Edmonton, we have a couple more examples. This one shows two types of barrier; a masonry wall in the background alongside a pathway (the pedestrian is walking on it, as on the Byron side) while on the near side against the road (Richmond side) is a barrier consisting of a two chains suspended between poles:
http://maps.google.ca/maps?f=q&sourc...329.12,,1,4.47
Edmonton seems particularly partial to this suspended double chain fencing, at least on their newest extension. Here's another example further south:
http://maps.google.ca/maps?f=q&sourc...2,75.08,,0,0.3
That fence isn't going to outright prevent anyone determined to cross from crossing, but it ought to give them pause before doing so. Still, I do wonder how the "think of the children" types would react to this.
I really doubt we'd be able to get away from fencing here in Ottawa. I would not be surprised if the Carling supplementary line ends up with fencing too. I think I would go with the Edmonton double chain fencing since it is the least obtrusive and acts least as a full barrier and more like a warning, but I don't know if we can overcome the fact that it can be overcome.