Solidity contract for superbowl squares

SuperbowlSquares.sol

pragma solidity ^0.4.15;
contract SuperbowlSquares {
    
    address public owner;
    bool public isLocked;
    bool public isRefunded;
    uint public squareCost = 0.05 ether;
    mapping (address => uint8) public squareCount;
    address[10][10] public squares;
    uint pot;
    address public winner;
    uint public r_offset;
    uint public c_offset;
    uint8 public homeScore;
    uint8 public awayScore;
    
    modifier onlyOwner {
        if (owner==msg.sender) {
            _;
        }
    }
    
    modifier lockable {
        if (!isLocked){
            _;
        }
    }
    
    function SuperbowlSquares(){
        owner = msg.sender;
    }
    
    function buySquare(uint8 _c, uint8 _r) lockable payable {
        require (squareCount[msg.sender]<10 && squares[_c][_r]==address(0x0) && msg.value==squareCost);
        squareCount[msg.sender]++;
        squares[_c][_r] = msg.sender;
        pot+=msg.value;
    }
    
    function setOffsetValues() onlyOwner {
        c_offset = random(block.number); //random enough
        r_offset = random(block.number-1); //random enough
        isLocked = true;
    }
    
    function setScoreValues(uint8 _home, uint8 _away) onlyOwner {
        winner = addressAtSquare(_home,_away);
    }
    
    function claimWinnings() {
        if (msg.sender==winner) {
            msg.sender.send(pot);
        }
    }
    
    function refundAll() lockable onlyOwner {
        isRefunded = true;
        isLocked = true;
    }
    
    function claimRefund() {
        if (isRefunded) {
            msg.sender.send(squareCount[msg.sender]*squareCost);
        }
    }

    function random(uint nonce) public constant returns (uint){
        return uint(sha3(nonce))%(9);
    }
    
    function addressAtSquare(uint8 _col, uint8 _row) public constant returns(address){
        uint colNumber = _col + c_offset;
        uint rowNumber = _row + r_offset;
        if (colNumber>=10) {
            colNumber-=10;
        }
        if (rowNumber>=10) {
            rowNumber-=10;
        }
        return squares[colNumber][rowNumber];
    }
    
    
}