That's a pretty tall order for an 8 acre lake. I doubt they would even knock a dent in it. I think if it were me I'd be looking more into Toulouse geese since they would be more apt to flock together and actively chase off most of the more common smaller threats. Of course they may well want to chase people away as well. I personally don't care for geese very much but they do handle their own business better than ducks and eat quite a bit more. If you're set on ducks, Muscovy are probably the best at taking care of themselves. But they are not a match for even raccoons.
Cheap fIve dollar size koi, butterfly koi, comet goldfish, common goldfish, shubumkin (calico looking goldfish), are all demolishers of duckweed, as well as the string algea that ridding your pond of duckweed will cause (much worse than duckweed). Muscovy will eat you out of duckweed. sadly my scovy which i only have out of the three, have eaten all my duckweed that the koi and goldfish couldn't get at that i thought had protected from. if you PM me id be really happy to get sent some duckweed, to try to grow some more for fish and duck feed (its like drugs to them and they'd eat till they were choking on). for birds though scovy breed really well and my males eat everything down (males eat even rodents up to med sized rats), like lawn mowing geese and brush eating mini goats. only trouble is they may stay away from places that have snapping turtles, which is smart, like mine are now (they can and do dig out snapper eggs and stop more from growing. each year old scovy female at oldest start to laying can hatch about one to two dozen eggs, and can raise those young up as long as has safe place to nest (you could just pen five females to brood and then when get restless with young let out. i keep dogs that protect property and ducks even ect, and have no fences, but train my ducks to come to me for food on command of whistling a tune, to be penned when need be, and catching for sale slaughter of too many males ect. if you don't penn them up when they begin to lay, they supposedly will nest in odd out of easy reach places. my extra male scovy are great sentinels and can gang up on cats foxes and dogs even and beat up or scare off of hold of from smaller easier meal females till my dogs get their. only trouble I've had are large wood rats. Foxes, weasels which one bit one male up who fended it off from his hatchlings. these only troubled them briefly when had young along with some BOPs they chase off. also.. some things i can't describe, but they came through and would only bother the scovy ducks for some reason.
creating floating raft island/s, with some sort of cover over part/s to stop BOPs should work for most preds but otter weasel coonand fox probly better than being on dry land will, but will deter really anything as can see better when resting, as my scovy fly away if they actually feel threatened (or they shuffle up around and under dogs). i don't feed my scovy when its green out unless locked up in pen, and haven't had any probs.