Sounds fine in principle but depends on the water that is feeding it (pH and clarity) and the level of insect life that is alive in it. If the latter is disturbed by the gravel and dig out then there may not be enough to sustain them and you may have to feed them pellets

I think it's racist that you went for rainbow instead of brown trout.

If you want to send me gps details of your pond I can take a view on the weather and terrain.  

And honestly not plan to poach them when they’re delicious and plump after mutters gives you a few months advice.  Muahahaha.

What a kind man you are laying on such a fine dinner for your  local herons

Interesting, thanks.  Gravel is only going around part in order to leave creepy crawlies in the muddy parts.  Water is very clear but I’ve no idea of the ph.  Will look at it.  Primary reason for getting bigger ones is to mitigate risk of avian predators but we’ve never had a heron around so it will be interesting (if costly) to see if the fish brings one in...

Again I have very good data on predatory birds, so feel free to give me map coordinates, I can check if it’ll be an issue.

While I look up trout recipes.

rainbow trout often tastes real muddy

Fish will taste muddy due to a couple of factors which include the warmth of the water as well as the number of organics, specifically algae in the water.  

It’s caused by a chemical called Geosmin which is especially prevalent in clay soil (due to absorption) and when algae is in full bloom.

Do not pay any attention to all these silly remedies about eliminating the muddy taste by the way, none of them work. The only thing to do is wait it out until the algae bloom is over and hope that the geosmin has sufficiently decomposed.  An old chestnut about washing or cooking in vinegar genuinely doesn’t work.  I have tried.

Hope that helps. :)

This.

i want to have problems like this.

Herons tend to take smaller fish as you mention, but also frogs, newts and, alas, ducklings. Anything the size of a chicken nugget or less.  They do not manage the larger fish but tend to leave them stabbed and fin-damaged. You can't shoot them on a general licence.

You want to worry more about cormorants. These coastal birds have pretty much given up with the hardships of the sea and recognise that easier pickings can be found in inland in private ponds, lakes and fisheries.  Again, no shooting on a general licence. People net trout ponds to deal with this. A group of cormorants will have all your fish in one night.

Geosmin is also the thing you can smell when rain falls on baked clay ground

PUBLIC HEALTH WARNING 

DO NOT SEND YOUR ACTUAL GPS DETAILS TO LOONIES ON THE INTERWEB!

Wibble, I told you to use that cream.  It only hurts the first few times, you’ll feel better about it soon enough.

My Dad has a pond, which used to be a swimming pool, with Koi Carp in them.

Whenever I go vist, the same ones I remember as a kid are still there, only much bigger. He had them valued once and you don't want to ask.

He's got a pump system which flows over rocks like a waterfall and a couple of cast iron herons standing over it all to dissuade any real ones.

And I'm not going to give Teclis any GPS co-ordinates.

You’re safe mate, carp are really not good to eat.  Unlike these delicious plump tasty trout that we are discussing.

You're a mindreader, Chambo.
 

You're dead right. I don't want to ask.

There's a resident cormorant at the old mill pond near us (filled by a part of the river that runs underground throuvh pourous rock).  It sits on top of the no swimming sign in the middle of the lake with an "I think I'll be the judge of that" look.