Let me say a thing: reservation is different from possession.
Reservation is when you say "reserve this thing for me, and tomorrow I'll buy it", if you don't buy within the term, you'll lose "the thing" for someone else to buy.
Possession is "it's mine; I bought it"; it's an acquisition.
In Simutrans, the land is yours when you build on, and no longer is yours when you destroy what you've built. ATM, you don't need to pay for land. If you do, who you will pay for when you start a game? Public Service? Simutrans is not a real estate game, OTOH I know, in real life, "cost of the land" plays a role in transport cost when you are building a network.
Reservation could be used when you want to build anything in a limited space, but you must use that space within a term/period (a day, a month...). If the period expires, you lose the reservation. I think this is the only way to avoid abuse of this tool *if* implemented. Reserving an area in possession way would not good because this could be used against others players, AI or humans.
Now about fences: I would like, even, fences were implemented officially in Simutrans or as add-on; not as "a way that looks like a fence" but an a new object, as I've said, a buildable ground-object. I would use it to close a highway or to delimit areas of the map, or to limit a city.
Also I feel the lack of farms and wide plantations; fences could be used here too.