Bronco if the water is cooler spring water it will sink to the bottom displacing the warmer water anyway. In that case I would keep it at the surface. The pond surface gives you the most oxygen, moving the surface water helps mix it. If the water is air temp already you may want to try something what like Kelly has shown. The goal is to move water with your incoming water.

In my case I have spring water coming in. At first I ran a 4 inch corrugated plastic pipe down to the bottom. I had to weight it down as air would get trapped in it. After awhile the air built up and the water would just back up the pipe. I now have it going through a 10 inch culvert at the surface that is open on each end. Air flows through the pipe with the water oxygenating it. It enters the pond at the surface and then sinks to the bottom. DO tests show this is best for my pond.

If you try to have it enter the pond at the bottom you will need to collect the water into a pipe much higher then the pond surface. You will need that head pressure to make it flow. Design it that there is no place for air to be trapped and use only smooth pipe.