The only problem I have is the great blue heron and recently the green heron. The green heron came once, the gbh has not stopped by this summer yet, it flies over every day. Last summer it came to visit every day. The chicken wire keeps it from standing on the side and fishing, the once piece of deer fencing down the middle keeps it from being able to fly in. I would prefer nothing, but those birds loved my pond last year. Nothing else has bothered the pond. The floating alligator heads seem to discourage the herons as well.
The gbh, two or three fly over every day, we must be on their roosting path, east in the morning, west in the evening, usually right over our pond and house, tree level. I know one of these days it will land.
Except for right at the walk out end it is deep enough to keep the heron from wading.
I draw the water just via piping no retro drain. The pvc we just put in (this weekend) is 3 inch, the end terminates about a foot off the bottom, netted with the plastic gutter net (some one on the forum suggested it) I have a retro bottom drain, just shipped from a pond I had torn down. I am thinking of installing it via a different pump to use occasionally to sweep the debris to the drain pump it into a leaf basket, then in to a skippy type filter, then right back into the pond, like a home made vac sort of lol. I have a ton of trap door snails, don't want a drain running all of the time. So far all I have done is net the bottom of the pond with a swimming pool net and pole, sort out the critters and toss them back in. Usually do twice in a summer, a good cleaning in the fall a good cleaning in the spring when firing the pond back up. To me easy maintenance.
The Dragon pump has a huge leaf basket, my skimmer has a huge leaf basket. I try to keep large debris out of the bog.
The pond is from 10 feet wide at the walk out area to around 20 feet at the deep end, about half plus is 5 feet deep, then decreases to 1.5 feet deep or so, the 1.5 feet deep area is only about 1-2 feet of the pond end. I made it so I can walk out or anything that falls in can walk out. The length is 26 feet. All soft measurements, I wasn't that concerned about actuals.
If you wanted a bottom drain going into the bog, well at least the way mine is built, I would have a pre-filter/settlement chamber to keep large debris out of the bog.