The original 20% suggestion for cover habitat usually applied mainly for the amount of vegetation for best production of pond fisheries. For artificial habitat I suggest 10% - 20% of the total shoreline length have cover materials other than or in combination with plants to provide resting areas, shade, and escape cover for fishes. These materials also serve as fish attractors.
Suitable materials include:
• Brush piles constructed with green cedar trees
• Other trees or brush if cedars are not available
• Clean rubble, cement blocks, and clay tiles or pipe.
All woody material should be weighted individually with rocks and sunk, or several branches or trees may be anchored together with concrete blocks.
Possibly the best attractor is comprised of a combination of several materials which provide both loosely packed and dense cover.
The location of the attractor is very important, but water depth is the single most important factor.
• Points of land which extend out into the water and then drop off rapidly into deeper water are good sites.
• Coves or other areas sheltered from the wind are also excellent sites.
• In small ponds, the area of deep water near the dam is an excellent spot for fish attractors.
• If your pond has a submerged creek channel a structure placed on the edge of it will usually produce good results.
Attractors should be placed in water so that the top is not more than four to six feet under water. See Fish IDing link below for best depths. The grouping of attractors is important; groups of three arranged in a triangular design seem to attract more fish than three scattered single units.https://mdc.mo.gov/sites/default/files/2022-02/fish_attractors_Jan2022_1.pdf
Good article from PB Magazine about cover and placement.https://www.solitudelakemanagement.com/blog/helpful-tips-when-installing-artificial-habitat/
Ideas from Indiana DNR.https://www.in.gov/dnr/fish-and-wildlife/files/fw-providing_structure_for_fish.pdf
For panfish utilize:
Pennsylvania Post Clusters Structure
Open Pallet Structures in groups
Submerged Trees and Brush Piles
Other options for natural structures include brush piles, submerged trees, or other natural debris. Turning these commonly found materials into structures are a great way to utilize otherwise useless scraps. You will want to place trees and brush piles in vertical positions rather than horizontal
and at a depth of less than 15 feet (figure 3). This will allow fish to be able to use the structure year-round. When structures are placed too deep, the fish are unable to access them due to the lack of dissolved oxygen. It is often helpful to anchor trees, either with rocks or concrete blocks. It is also more effective to group trees to make a larger brush pile than having individual trees spread out. Submerged trees can provide excellent habitat, although not for an extended period. For example, Christmas trees are often used in ponds and lakes as a habitat option but decompose relatively quickly.
Good lengthy lesson of fish habitathttps://www.fishiding.com/recent-fi...tractors-which-do-the-fish-need-and-why/
The idea is to create as thick and complex a jungle as possible. The final result will resemble a thick mass of long branches extending from the dense pack inside the habitat unit/s. The branches should reach from every depth of every unit in every direction and at every possible angle. If your finished habitat unit looks even vaguely tidy, it needs more work.
Underwater diving studies have shown that artificial habitat of which the fish prefer most, stands a minimum of 1/2 the water depth, with 2/3 or more being much better. Objects standing from bottom to surface were utilized most by the largest number of fish, bugs and creatures.