Placing an Object in front of fence, behind fence

How Do I place an object (Animal, Ball, Person, etc.) that is outside or in front of a fence to appear inside or behind the fence

some pictures would be usefull. Then we/you can go from there.

Layers and transparencies would be my guess. Post a few of your pics, we can then elaborate.

You've got quite a big job to do.
You'll need create masks selecting the fence, then copy it onto a new layer, dont forget to fether. Then you'd place your animals on different layers (behind the fence / in front of the fence). masks, masks, masks, fether, fether, fether.
Good luck

Thank you for your response. Can you be more specific on the "How-to" (If you can) in step-by-step format

2 ways to go about doing this:

1) If the image you want to affect does not already consist of people, etc. in front of a fence, but rather you are combining two images, then a layer mask is the best solution. Using the Move tool (type "V"), drag the people, etc. on top of your fence image. Position it where you want it and create a new mask (click the little circle-within-a-square icon in the Layers palette). Now, use either a paintbrush, or a marquee, or something to fill in black wherever there is fence and white wherever there is not. Black on a mask means that part of the image is invisible, and white means it is visible (and varying shades of gray vary the opacity). I suggest using a small-ish brush with some soft edges to paint black onto the mask wherever the fence is, but you can do it however you like... another method is to select the fence with the lasso, click on the mask in the Layers palette, and fill it with black with the bucket.

2) If the people, etc. are already part of the image, you will need to recreate part of the fence to look like it is in front of them (do this on a new layer). Unfortunately, I don't have time to go into depth on this point... perhaps someone could take over?

Usually when you recreate part of the picture, you want to use the rubber stamp tool to make it look as realistic as possible. Option-click(or alt-click, i think, on pcs) on an area that looks like the part that you need to reconstruct, then left-click and drag over the spot. It's hard to explain, but easy to see once you work with it.
Otherwise, you can copy part of the fence, paste it, and apply either a gaussian blur or use the blur tool. Either way is fine.