"Ben" wrote | Hmm, sounds expensive. Also, they've done a pretty good job | of vandalising some brick walls round here lately by throwing | rocks at them - huge bits fall off. I actually do care what | they do to the other side, as I have to walk past it every | day. I'd like to be able to see what they're up to without | them being able to climb over. Hence picket fence with pointy | top, or lowish spiky hedge. The house on the other side of | the footpath has a hedge and it hasn't done the tarmac | footpath any damage, although its planted in soil, not holes | drilled into the tarmac.
It won't be cheap, but I'd suggest some type of industrial metal fencing - the sort used on industrial estates to keep scrotes out. One popular type has pressed metal verticals rivetted on to metal rails, set in either metal or concrete main posts. The rails are on the inside, and the verticals are pointy at the top, so it is very difficult to climb on/over, and because the verticals are convex and metal they remain rigid and rather painful if anyone tries bouncing off them. It's available in various colours, a dark green is fairly smart and visually unobtrusive. You could then plant your seedlings inside, you can get special biodegradable tubes for protecting saplings. Without a fence your saplings will get vandalised or stolen.
Digging holes - if you are in an agricultural area it shouldn't be too difficult to borrow or hire a Post Hole Borer.
Owain