How to play
Draw fences along the grid lines to divide the whole board into paddocks. Every cell belongs to exactly one paddock.
A paddock is any connected group of cells — you can walk between any two of them through shared sides. It can be any shape at all: an L, a T, a zigzag or a plain rectangle.
Every paddock contains exactly one number, and every number belongs to exactly one paddock.
A number is the length of the fence around its paddock, counted in cell edges. A single cell’s fence is 4; a 2×3 block’s is 10, and so is an L of five cells.
The outside edge of the board is always fenced, and those edges count towards a paddock’s fence length.
The puzzle is solved when every cell sits in a paddock holding exactly one number equal to its fence length. Every published Fence It Up puzzle has exactly one valid solution.
Read the number as a size range
A fence never tells you the shape, but it always pins the size. A paddock of n cells has a fence of at most 2n + 2, so the number is never more than that — and its fence is never less than twice its width plus its height, so a big number cannot belong to a tiny huddle. A 10 holds 4, 5 or 6 cells; a 12 holds 5 to 9.
Example: A 10 sits on the board. Whatever shape it turns out to be, it covers at least four cells and at most six — so a neighbour two cells away is well within reach and one six cells away is not.
Take the 4s and the 6s
A 4 can only be a single cell: fence all four of its sides at once. A 6 can only be a domino — two cells, in one of four positions around the number. These cost no thought and they seed everything that follows.
Example: A 4 sits in the middle of the board. Fence its top, bottom, left and right straight away; every neighbour belongs to some other paddock.
Separate two neighbouring numbers
Two numbers never share a paddock, so the line between two side-by-side numbers is always a fence. Sweep the whole board for those pairs before you work anything else out.
Example: A 6 and an 8 sit in side-by-side cells. Fence the line between them immediately.
Give a cell to the only number that can reach it
For every empty cell, ask which numbers could still grow a paddock as far as it. When only one can, that cell is that number’s — and that usually rules out most of the shapes it had left. A cell no number at all can reach means something earlier is wrong.
Example: A cell in the corner is out of range of everything except the nearby 8. Weld it to the 8 with an open mark and see what that forces.
Shapes are free — stop looking for rectangles
A paddock can be an L, a T, a zigzag or a staircase. When a rectangle refuses to fit, the answer is usually a bent shape reaching round a neighbour, not a mistake further back.
Example: A 12 has no room for a 3×3 or a 2×4, but an L wrapping around the paddock below it has a fence of exactly 12.
Count the cells that are left
The paddocks tile the whole board, so their sizes add up to exactly the number of cells. When most of the board is settled, the leftover count often rules out every size a number could still be but one.
Example: On a 6×6 board the settled paddocks cover 30 cells and one 10 is left. It could be 4, 5 or 6 cells — but only 6 finishes the board.
Use the open mark as a real deduction
The open mark says “no fence here”, which means those two cells share a paddock. That is an argument, not bookkeeping: it joins the cells for good, so an open mark between two numbers is an immediate contradiction and the board flags it.
Example: You know a cell belongs with the 12 beside it but not yet which shape. Mark the border between them open and the two stay welded together as you work.
Never let a fence dead-end
Fences separate paddocks, so at an interior corner a fence either turns or carries on — it can never simply stop. If three of the four lines at a corner are ruled out and one is fenced, something earlier is wrong.
Example: A short fence stub sticks into the middle of an open area with nothing to meet. Extend it or remove it; it cannot stay as it is.
Read the paddock colours
A closed area with no number in it turns red — no number can ever reach it. An area with one number goes green when its fence length matches that number, and red when it does not. An area still holding two or more numbers is simply unfinished and stays plain.
Example: Fencing off a corner leaves a 2×2 block with no number in it. That block turns red at once — undo the fence that closed it.