There were news (and interviews) in 2017 that Lithuania was building a (2m tall) border fence with Russia's exclave of Kaliningrad. Wikipedia's article on this is woefully out-of-date as it only says Lithuania had "announced plans", although you can see in the DW interview that they were advanced as far as planting poles for the fence in at least on region.
There's also some confusion (at least in my mind) as to the length of this fence. Wikipedia says the Lithuanian-Russian border spans 275 km. But one Lithuanian article from late 2017 said the fence had been (declared) completed "after six months of construction", but that it span only 40 km. Furhtermore a BBC article from early 2017 said that "The fence will cover 130km (81 miles) of border, from Vistytis to the Neman River, which runs to the Baltic Sea."
So what length does this fence have, as of 2021?