The electrical fencing is still a good idea. We don't have deer here, but we have moose, and the first year my parents planted
apple trees(6'), a moose came right into our yard and 'pruned' the tree's for us.
But for smaller pests, that's going to be an issue. Especially because your doing a mass planting, sounds like 1000's of trees, a lot of things aren't going to be cost effective to you.
People try a lot of different things to protect against rabbits, etc.
Most people around here resort to making cages out of
chicken wire and
kindling wood stakes. Or snow-mesh, plastic orange netting, etc. Or it's normally neutral enough around here that they just leave those fabric shrub protectors over them all year round.
But there's also the plastic tubes used for weeping tiles, the black corrugated plastic tubes that can be cut to any length and then a slit put in down the side so you can just slip it around the tree trunk. Small pieces like this could easily protect a sapling for a year or two depending on how well they grow.
Some people have simply resorted to buying snow slides(the plastic sheets), and ziptying them into tubes, mainly for dog protection for a few larger trees.
For saplings, plastic
milk jugs or 2lt bottles etc, with two horizontal slits made in a side will let you put a wooden stake thru it to secure it into the ground over a sapling.
Some people make sleeves from thick plastic bags(sandbags mostly, with the bottom cut off), and making a triangle or square out of wooden stakes. Labour intensive, but for the cost of kindling(free) and a box of bags(34$/100, or 187$/500), they work out to be about 36 cents without the labour, and that's from
online hardware store quotes, I'm sure you could find them cheaper from an actual bulk store.
That doesn't help if you have issues with moles/gophers, etc, from
underground. I was once told that the issue with the underground critters is that they can sense the disturbed ground where you insert a tree, usually because they punch thru and impede on existing tunnels. There's no real way to protect against them, especially for small saplings. For larger trees or shrubs, when I lived in BC, I witnessed a person try and resort to actually digging holes to big for the tree, lining it with a
chicken wire cage, and then back filing with small stone and pottery shards before putting more soil and planting the tree, then making a big cage out of a tomato cage wrapped with a fine wire screening mesh (admittedly this person was a bit, shall we say Kamloopy, but they'd just lost 5 combo espaliers to voles).